It could be either one. it may be your tranny not doing its job 100% or it could be that your clutch could be bad. but you'd have to really look and see whats wrong, before you even atempt to try replacing something, when it could have been the other. then it'll have cost more.
Clutch pedal.
The clutch arm is like a teeter-todder. The clutch arm sits on a pivot point in the transmission bell housing and disengages the clutch by pushing down on the pressure place through a "throw out" bearing when the clutch pedal is pushed down.
manual transmission , with no clutch pedal .
The clutch pedal is the one left of the brake pedal. The clutch disk the pedal affects is inside the transmission bell housing where the engine block bolts to the transmission. Unless you have an automatic, then your car has no clutch.
That would be a standard transmission.
A manual (standard) transmission.
Transmission Input Shaft
Transmission Input Shaft
The clutch safety switch keeps the car from starting unless the clutch is pushed in. On the top of the clutch pedal there is a little black box with a plunger on it. When the clutch is pushed in the electrical connection to the starter solenoid is completed. The switch just unscrews from the bracket.
You may try checking the clutch mastercylinder for fluid level. It will be located on the firewall close to the brake mastercylinder. If it's low, it will cause the transmission to grind instead of going into gear. It could also be bad. You can tell by having someone depress the clutch pedal while you watch the clutch slave cylinder to see if it's expanding. It should move out when the clutch is pushed. If those two things work and the transmission oil is at the correct level then you've got an internal problem.
The clutch safety switch is on the clutch pedal shaft. It is a small black box with a plunger coming out of it. When you push the clutch down, the clutch safety switch connects the starter and it should turn over. If it doesn't you may have to replace it or adjust it. It's adjustable. Just adjust it until the red plunger is fully retracted out of the switch when the clutch pedal is pushed in all the way.
If it chatters when you start up I would be concerned. If some of the gears do not work, the clutch may be the problem.If the pedal is too low to the floor or gears strip or grind when you shift, it may only need adjusting.Fortunately, compared to automatic transmission, clutches are cheap to fix.