Who am I meant to stick around as adc?

Stay as far back as you can and shoot whatever is closest to you.

the one with the most peel, preferably a nami/janna, or your sejuani/nautilus. its imperative that you stay alive and get free hits off without restraint.

sometimes it is better to stay at base than venture into your own jungle alone, or back to lane looking for farm.

Stay near the tank on your team, the tank is your friend. That why I go Garen top, because I can protect the ADC and do damage. The other team is going to target you first so stay in the saftey net, and always have map awarness.

anyone that can or in most cases "is willing" to peel for you. Look for qualities like stuns, slows, displacement, and general tankiness. These are usually your peelers. Typically your support has one role in team fights and that is to peel for you...if you are looking for others to do it, your support blows.

just try to stay in the back. if your team is good, they will try to stop anyone that jump on top of you.

stay behind the tank

If you want to learn how to ADC, I'd suggest playing AD Corki at mid against a Zed player.