Unless you are a melee / near-melee character laning against a ranged character, "just standing there in the rear" will basically ensure the enemies you are laning against get fed to holy bejesus. Even most melee heroes can harass baddy ranged players effectively. The issue is you get bonus gold for enemy champion *and* minion kills, and if another player is constantly hitting you, it becomes dangerous to get close enough to minions to get kills, thus stopping you from preventing the enemy champions from getting last hits and lots of bonus gold themselves. Unless you're playing a character with mad life steal or healing abilities, once you run out of potions, it becomes almost necessary to go back to the fountain to heal as nearly every character is super squishy early game. If you don't go back, you die, and that's even more money the enemy team (especially the player who killed you) earns. You just have to remember that a combination of three things win this game: team skill, team champion selections, and items. Let an enemy carry get too many last hits and you will get dominated by that carry later on.
More or less the goal of early- and mid-game LoL is to beat the snot out of the enemies you are laning with, stay alive (and in good health) yourself, and last hit minions. If you can get a hero kill, that's great, but it is not worth running into tower range or tanking creep waves. It makes me QQ a little every time I see a newbie Ezreal in a matched game run after a severely wounded enemy only to get two-shotted by a tower. If you aren't comfortable yet with how to properly go about laning, remember, there are practice games there that still earn good experience and IP. Don't be afraid to play them. Just don't play against bots. It doesn't hurt at all to lose practice games, but you'll never learn anything at all playing against bots. (They're just free IP basically.)