Where should I try to center the weight? My initial reflex is to fall forward so I end up getting on my toes, I try to force myself to keep my feet flat on the ground and it goes to my heel.
I figured my shoes weren't helping so I tried barefoot and the same thing happened.
The weight should be over the middle of your foot, because you want your center of gravity (which will be exactly over the middle of your foot) to move perpendicularly with respect to the floor.)
Here we have 3 different squat variants (from left to right, front squat, high bar squat, low bar squat). Notice how the center of gravity is always perpendicular to the floor (dotted line) exactly over the middle of the foot regardless of bar positioning. Thus, the back angle changes to compensate, from almost upright in the front squat, to almost 45° of lean in a low bar squat.
If you are interested in learning how to squat, I
urge you to get Starting Strength and read it thoroughly.
And no, you may not use the smith machine to practice. That'd be analogous to trying to learn to play guitar on a Casio keyboard. Smith machines are only good for leaning over when resting between sets or for hanging towels / sweatshirts.
