Could be a number of things, check your your Transmission Fluid, if the level is fine, it may be your transmission or clutch. Most likely your clutch, which is cheaper than a transmission.
The shift cable is loose or mis adjusted.
Shift cable adjustment, low fluid, internal transmission failure.
car will jerk forward and then go in reverse
A plugged transmission filter can cause your transmission to hesitate when you shift into drive. A collapsed vacuum hose can also cause the problem.
are you pressing the brake as you try to shift?
does it shift into reverse and wont drive? if so its your tranny it needs to be replaced
There are several things that can cause your manual transmission not to shift out of first gear or reverse. The most common cause is a broken shifting fork.
You need to have the system checked for codes. Any electrical problem with the trans can cause a no shift.
You have to step on the brake pedal to shift to any gear from "Park"
The gears in your transmission may be sticking or worn out. This would cause your transmission to not be able to shift.
Generally shifting from reverse to drive, while still rolling, is possible but not recommended. This places a lot of stress on the transmission and other components of the drive train.
Park, reverse, neutral, Drive and low