-First check transmission fluid. If none or it's low , top it to full indicator and try to drive.
-When check the fluid, engine must running and hot or normal temperature..
If fluid is full then next you need to check the shift cable to the control arm. Is it moving when you shift to D and other position...? If No. then possibly the cable to the arm is lose. If yes it move as you shift, then it's time for new transmission.

Good Luck.

Mai