Its actually very simple. A pot has a range from 0 - 1023, and being that you want to control a motor or servo, you will most likely want full forward, full reverse and stop.
Well forward is equal to anything above 512(mid point of pot), and reverse is anything below 512. Now you also want to stop the motor, and that done when your at 512.
So you will need an IF statement.
psudo:
int XSpeed = analogRead( XpotPin );
if ( XSpeed > (512 + deadzone) ) //go forward
...
else if ( XSpeed < (512 - deadzone) ) //go reverse
...
else //XSpeed = 512 +- deadzone, stop
deadzone is needed because your pot will almost never perfectly be centered at 512, so some slack is needed