Read about all the heroes and find one that sounds good to you...then play him. Seems like you are looking for the OP classes..and sadly you will find them if you read the forums or the odd views on OP some people have.

I personally like Zilean, Taric, and Teemo.

The point of the game is to blow up the main hub in their base. This will require that you clear all the towers from at least one path and usually involves killing players.

As for which hero is best, I think it depends on your mentality I think but just learning the game and coming to understand the cause and effect of different actions is far more important than your character choice.

And for that, there's really not substitute for experience.

runes are an experimental feature right now. they give slight boosts to various statistics. they aren't reallllly necessary to play the game.

you unlock your ultimate at level six. In case you haven't figure it out, you start off at level 1 every match. there are also limits on what abilities you can choose at which levels. i do suggest just playing around and figuring it out. ignore the people yelling at you for being a nub.

Hmmm...well, there is no best. There are certainly OP heroes, but that doesn't mean that they're uncounterable or that they won't be nerfed. With all the people crying about Jax, I'm almost positive he'll be nerfed in the next patch. Maybe a hotfix, even.

Like some of the guys above me suggested, pick a champion who appeals to you. Someone who looks interesting. Then, play a few practice games; all with that champ. When you feel ready, take it to solo queue and have a few matches with that champ. Once you got the hang of him, you can move on to new champs.

There really isn't a point per se. It's for fun, really. You know? Like games are supposed to be? :/

By point I think he meant objective. The objective is to kill the other enemies main structure(nexus). I highly recommend you play a practice game or two just to learn how to buy items and whatnot. Once you do, you should look at guides as well so you can do the correct thing for a certain hero.

You should play defensively when you first start, stand back by the ranged creeps, keep an eye out for what's going on, and make mental notes of what each hero does, so you can learn to expect it in future games. I'd also strongly suggest you play games with your friend so he can lane with you and hold your hand the first few games until you understand what to do.