the basic gains define the sensitivity (how aggressively or sluggishly) the autopilot uses to keep position with gps. the higher the number the more zippy it will be to hold position, the lower the squishier it will be.
the attitude gain controls sensitivity for pitch and roll of the sticks on the transmitter.
ive seen conflicting (or at least ambiguous) information on whether there is any interaction between control sticks (transmitter) and the yaw or vertical items on the basic gain row. but i cant find the thread on it due to limited search capabilities here.
zippy, faster reaction, more aggressive.
if gains are too high you'll get oscillation since it over corrects thus has to correct in the other direction .... and so on. It's like turning too far and too fast on a car steering wheel in a curve,
the best way to understand it isaiah is to increase and decrease it 10% or some small amount from where it is now and test fly both positions. you will notice the difference in how it hold position.
Well then feel free to play around with the gains but you'll likely find the stock values very close to ideal unless you made modifications to your bird ( weight change, different motors / props,...)