Does the old iphone 3gs auto backup evertime you plug in to your phone to your computer?

I had an old iphone 3gs in 2010 and would plug it in but i don't know if anything got backed up, i'm trying to get a new ipad now in 2015 since its been so long since i've used apples products, trying to see if that will restore all my old info on my itunes account music etc…

Depends on your iTunes settings. You have the option for that if you want or could turn it off.