Q: My clutch won't let me shift into gears, and my clutch feels soft when pressed down.

Here's my issue, I can't shift gears when I press down the clutch. Instead when I try to shift, it doesn't go into gear and I hear a loud gear grinding noise every time. Although I can shift when the car is off and it moves. I checked my reservoir (which holds both brake/clutch fluid) and it was on the minimum line. I filled it up, and so far it hasn't drained any fluid. Certain people tell me it's the master clutch cylinder and some people say it's the slave cylinder, but I can't really tell. There might be air in the rubber tubes, that doesn't give pressure for the gears to switch, I don't really know. Yesterday my friend (he's a forklift mechanic) inspected my car and we noticed there was a leak under the rear left side of the car. It was probably leaking from the hose that's connected to the rear left caliper for the wheel. He said it might be a busted brake line or a brake hose. That's probably what's causing the whole issue with the clutch system.

My car has 180000 miles.
My car has a manual transmission.