Your car might have a hydraulic clutch that is low on fluid.Open the hood and
look on the fire wall where the clutch goes through.If you have a small round canister check the fluid level.
It does sound like the clutch is not releasing when pushed in.I had a problem about the same,but i had a broken spring on the clutch plate.It would shift fine with the car off and not at all when running.
If your car is a cable operated clutch you can find the clutch cable and follow it down to the transmission,turn the black knob to adjust.Mark