What is the possible reasons the vehicle doesn't shift gears easily; or at all ? on 2001 Suzuki Esteem

The car is a manual transmission.
Recently started to struggle to get the car in gear.
Will shift easily when engine is off.
Has to be forced at times to put in gear, and other times shifts normally.

Asked by for the 2001 Suzuki Esteem
Check fluid in clutch mast. Cyl. Clutch adj.,worn clutch, trans. lube.
1 more answer
ck all fluids incl trans fluid level and that it is clean