so when i thought about buying a mixer, people told me don't because when you record it makes everything on one track. so if i was recording with an interface, and i had 2 mics recording at the same time, would it split the recording into 2 tracks?
Yes, and no. Look at the product details and see if it offers individual track recording options, or just a stereo mix. For the most part, an interface will output individual tracks, but just do a little research to be sure.
Yes, if your interface handles 2 inputs at once, then you can just add 2 mono tracks (one for the left and one for the right) or you can set it up as 1 stereo track.