Alrighty, my reply's likely to be fairly lengthy, hahaha, but I've read your post and am working on it now, it's comin! XD I'll just edit it into this
Alrighty, we'll start off with the "meta". The meta is the player enforced typical team comp believed (and usually proven and accepted) to be the most effective. It's what you'll encounter most of the time in ranked matches and what your team will expect you to help put together. The meta is generally a mage (AP) mid, a ranged AD carry with a support bot, a jungler, and a solo top. We could take forever delving into the exceptions and hypothetical scenarios, but in a nutshell, that's it. Usually in draft mode, as the team joins the chat, people will call out what they'd like or what they're best at. Good and polite players are flexible, but you will occasionally run into those with the "mid or feed" mentality. Sometimes your team will recognize the rule of "dibsies", lol, allowing whoever called a role fist to play it, but more often than not, if they're above you in the pick order, they'll take what they want whether it was called or not. Now, the purpose of draft mode is to counter pick the enemy team to the best of your ability, this is where the meta can become a gray area. Say a Kassadin or a Galio is the enemy mid, in this case it's actually not unwise to put an AD mid, as those 2 champions can shut a mage down. Talon's an excellent choice for such a situation. This is something that you'll only learn in time by playing and taking the advice of others. You'll just need to start learning which champs are good/bad against others and with that knowledge communicate and cooperate with your team to build a good comp. Generally any team with a solid amount of CC is good, and you want to try to have a solid team fight initiator like Leona, Rammus, Malph, Alistar, etc. You know, someone beefy with CC that has an ability to quickly put them in the center of the fight ahead of the team and abilities to disrupt enemy damage output. This of course would typically be called a tank.
Now support can be a little more difficult to define, but generally, whoever is NOT the ranged ADC (AD carry) bot is expected to be the support. The support is expected to take little to no creep farm, allowing the ADC to farm up. Their income is arguably some of the most important in the game as they are usually the best, or one of the best, high sustained damage output and are item dependent. So, the support needs to do just that, support the ADC. They should be trying to zone the enemies, to keep them at distance so they don't disrupt your ADC's farm and can't farm well themselves. Supports are typically champions with heals, buffs, debuffs, and CC, someone who can make their ADC stronger and sustain them in a fight by backing them up with said heals and buffs, or someone tankier who can initiate and set up a kill for the ADC while trying to protect them. I would say I actually main support, my two favorites being Leona and Sona. And when you choose your support, choose it based on what your team comp needs and what your enemies chose if you can see that at the time you pick. So, if I'm on a team that already has beefy champs and good initiation, I'll choose Sona, if our team is lacking tank/intiation, I'll choose Leona. While technically any champ CAN support, you generally want it be someone with the ability to set up a kill and/or sustain their ADC. And you'll want to try to choose a bot combo with good synergy. Some support buffs do more for some ADC's than others. Again, that's another thing you'll just kind of learn as you go and gain experience and insight.
Oh, one note I forgot on support...as you won't generally have the opportunity to farm for gold, you'll want to buy a couple Gold per 10 items...Philosopher's Stone, Kage's Lucky Pick, Heart of Gold etc, the choices will vary depending on the champ you're playing. If/when you can afford it, doesn't hurt to buy the Gold Per 10 quints and to build a page with points for gold bonus on assists in the Defense and/or Support mastery trees. But, moving on.
Top and Jungle are very flexible roles and have a wide variety of champions that fill them. This is where counter picking and team comp really matter, choose the champs for those roles based on that criteria Junglers tend to mostly be tanks and bruiser/fighters though, with a few AP. Top should generally be someone who can fight well in a 1v1 situation with good sustain and either solid survivability or mobility. A few good example of common top laners are Garen (as mentioned earlier), Shen, Wukong, Yorrick, Darius, Jayce, Riven, Shyvana, Fiora, Vlad, Teemo, Kennen...the list goes on. Teemo's a good counter to AD's because he can blind, slow, and speed buff himself. So he's got good ranged harrass with the mobility to survive and escape. Kenne'ns mobility, the fact that he doesn't use mana, his high range harrass and CC also make him a good counter pick to most melee bruisers. If you're looking for someone like Garon, hm...that's tough, but I would suggest perhaps trying Wukong, Tryndamere, or Darius. Yorrick is also a very a strong top, though nothing like Garen. He's very difficult to counter though. For a jungler you typically want someone with high mobility and CC, so they can quickly leap out to initiate/join a fight before they're seen and pin down the target. Examples of this would be Warwick with his ult, Malph with his ult and slow, Diana with her gap closer and slow, Lee Sin with his little kick leap thing, Shaco, Twitch, and Evelyn due to their speed and stealth...once again, the list goes on, just a few examples of common choices and why they're good. And, as always, this is just another one of those things that just comes with time, with learning all the champs and their strengths and weaknesses.
The key to it all when it comes to draft (especially ranked) is going in with an open mind. Don't go in with the mentality "This is the champ/role that I want, and this is the champ/role that I'm gonna play!". Go in with the ability to play a few champs and a few roles well, tell the team what you're best at, how you'll best serve them, and more often than not people will want you to play to your strength. You'll want to try to build a team that has a balance of beef, CC, AP, and AD. Communication and being polite and constructive is critical at champ select, it can set the mood for the whole game. You'll have games where you know already in select it's probably gonna suck because your team is already squabbling. So, try to set a good example and foster and encourage communication and cooperation.
One last note, summoner spells are highly debatable, but there are typical standards you can go by. It's common for the ADC bot to take heal while the support takes exhaust, because odds are, the ADC will be their first focus and more in need of the full heal effect. Personally I feel heal's a bit of a waste, it's not terribly useful mid-late game. It's prudent to always pick a spell that offers you an escape, such as flash or ghost. Teleport is common for Shenn and TF and top laners, though I don't use it very often myself. Ignite usually works well on most AP's, Exhaust on most AD's (being able to slow them so you can continue chasing while maintaining range to auto attack while reducing THEIR auto attack damage as you're likely facing another AD), you generally don't want Ignite on a champion with an execute...like Garen and Darius...because if timed correctly, your ultimate will kill them and you won't need the ignite. And you want a mix of exhaust and ignite on the team as using them correctly can be invaluable in a team fight. When team fights happen, you can exhaust their heavy AD hitters and ignite champions with a way to heal while in combat, as the ignite debuff reduces healing effects.
That's about all I can think of off the top of my head, haha, sorry for the novel, but I sincerely hope this helps. If you have any questions or need any clarification (I prob typo'd or just derped and said the wrong at some point XD), let me know!
Best of luck and happy hunting! See ya on the fields of Justice!