G'day,
It's an Hydraulic type clutch, so the first thing to check is the fluid level in master cylinder.
This will be under the bonnet beside the brake fluid resevior
If the level is low, then top it up with brake fluid.
The clutch should now work again, but it does mean you have a fluid leak.
Usually it's in the slave cylinder, fortunately these are quick, cheap, and easy to replace.
If the level isn't low, it may still be the slave cylinder, but you will need someone to work the pedal while you watch the cylinder to see if it's moving and release fork.
If it is, then the problem is with in the clutch itself.
It's not unheard for the diaphragm on the backing plate to fail, or the disc to stick the flywheel, break etc.
That is a bit more involved to fix, as it does mean removing the gear box and replacing the clutch.