I'm trying to install gentoo but i don't know what to choose, whats the difference, and how do i know which one to choose?

i'm pretty sure that the x in x86 is a variable so that it could mean i386, i486, i586, i686, etc. But i could be wrong. Im sure someone will reply and correct me if im wrong. Are you on a linux system right now and going to switch to gentoo or are you coming from windows? If your on a linux system right now you can do uname -m to find out.

as you can see on mine it says i have i686, but honestly im not sure how uname gets that info - like if it pulls it from something that reads the actual hardware or if from something that the distro installed, so maybe if i installed the i386 isos it would say i386 instead. Im pretty sure if you had 1686 that it would be safe to choose either i686 or x86 but if you know for sure it is best to match your hardware as close as possible, but like i said someone would have to chime in and correct me if im wrong about the x in 86 just being a variable because im not 100% sure.

I think uname get's its information from the kernel, which probably knows what processor you're running. It is safe to use both. It might also give you an ever-so-slight performance advantage to use i686. All it means is that if you want to take one of your programs and run it on an i{3,4,5}86, they might not work.

Depends on your CPU.

This has been asked a billion times so if you search you'll get a better answer, I'm not typing it all out again but i686 is better than x86 for a 32bit Intel-compat CPU that is newer than Pentium Pro and AMD K6.