My swisher mower starts but will not move when the stick controls are pushed forward or backwards.

Remove blade drive belt. turn each blade by hand. Sounds as if you have bearing problems. Each spindle has an upper and lower bearing of the same size. They are notorious for going out! You can get them at most any auto parts store. Also check the tensioner pulley bearing. They go out quite often. As for the jerking, make sure the two drive disengage rods are fully in. Check tension on drive belt and belt. These belts get worn quickly. Be sure to blow the trash and dirt from your mower after each use. Especially the Hydraulic motors and the mower deck. This will save you lots of trouble. If you wash the mower, be sure and run the blades and Hrdroes to get water dried from bearings and pulleys and belts.

Belt routing. Double check against the manual.

Was it working correctly earlier or is this your initial operation?

According to the product manual for "loss of drive":
1. Bypass linkages in the bypass position
2. Hydro belt worn, damaged, or broken
3. Idler spring loose or broken

1. Make sure that the bypass linkages are in
the drive or engaged position. Located at
the rear of the machine. Refer to decal on
the rear of the unit.
2. Replace Hydro belt.
3. Replace Idler spring

Your drive belt is off or slipping.

Check the adjustment on the accelerator linkage. Make sure it is fully engaging.

Check your drive belt that it has not slipped off the drive cog under the motor. Also check the alignment of the motor with the handle on the right side (speed, reverse, and neutral lever).. This lever tilts the engine to engage the drive belt.. there is no transmission in this machine.. just how the belt engages by its angle when you push the lever forward and backward.. If the engine is running, it must be either the belt to drive the unit or the angle has been messed up somehow..

did the belt break or fall off?are the push control rods pulled out to push it ?

check the lever on the rear of the tractor used to puch the unit when not running then check the belt

1) The drive belt between the engine and transmission has broken or jumped off a pulley.
OR
2) Your hydrostatic transmission is dead.

DO NOT STICK YOUR FINGERS UP INSIDE A RUNNING MOWER TO SEE IF THE DRIVE BELT IS MOVING.

You do not change the wheel height, you change the cutter height,there should be an arm sticking up neart he rear wheel, you just push it to the side a little and push it either forward or backward.
Hope this helps