Eh, it's a right enough place.
First, things first; don't worry much about how you do. Just learn and don't worry about. You should see how I played when I was level 6 (No, you shouldn't actually; it would cause physical pain) Right now, you just need to have play and have some fun while you are at it.
There are two things, there are Ranged AD champions and ADC (the role). The purpose of the creation of the ADC was that it was found to be useful to have a dedicated player to provide and who can provide sustained DPS throughout the team fights. Attack damage is the easiest way to get this, because of the consistency and reliability of Auto-Attacks, as well as other bonuses such as that the stacked AD does more damage to towers, most abilities do not. So you would have one player who would focus building all damage, and the others would protect that now vulnerable player and in return, the ADC functions as their little, orbiting, arrow pod.
So the ADC gets put in the bot lane with another player to babysit so they can farm for the high ticket damage items and don't get squashed by enemy players.
I tell you this so you can pick up what the ADC is supposed to focus on. The first is that the ADC is to learn to last hit. I know you said you know this, but I am saying it again for emphasis. All roles need to last hit and it is important, but for the ADC it's even more so. While some champs can get along with relatively little gold yours are expensive, just one of three parts of the Infinity Edge is 1550 gold, not only is it a lot but it's a long amount of time where you are not progressing, can't buy much at all, if you are looking to buy it. The shorter your time to an item, and consequently a power spike the better. Rule 1: Go for the Gold.
As was also alluded to, because you are putting all your resources into damage and not defense or survivability, you're very vulnerable. Maybe even more than the mages, because a lot of there items have in built defensive stats while yours aren't available. So we come to next one. Rule 2: Stay Safe.
As the squishiest person on your team, you need to always be sure to be safe. Use your range, it's one of your best advantages. Stay with a good buffer zone between you and the enemy, especially with teammates between and continue to constantly attack to deal damage while moving to stay away from taking it yourself. If you go down, not only do you all lose a member from the teamfight, but you all also lose a huge chunk of your DPS. And you have to be careful because this reason makes you a target as well.
This leads to the next rule. Rule 3: Mind your positioning. Positioning is important for all, but again it's perhaps more important for ADCs. It's what you have to pay attention because it's the primary determiner of whether you are dealing damage or taking damage. Be aware of not only where you are, but where your allies are, where your enemies are, and even where your enemies might be. You also need to stay aware of *who * your enemies are. If you are in lane CSing and 
or 
have a straight line down lane to where you are standing with none of your minions in the way, well you better fix that posthaste. Along the same lines, mind where your lane mate is. Even if they are only a thousand units away, that's still three seconds before they can help you. You can accidentally find yourself into a 2v1 fight without even realizing it. Similarily, it applies to the enemy, if he strays to far for that caster minion, you and your lane mate can use that for great engage.
That's good for now, I suppose. You can respond if you have more specific questions.
