Transmission will not shift into gear

One day it wouldn't start. A week goes by and then it magically started but now when I try to shift it into gear any which way it starts grinding. I have not tried to force it into gear because I don't want to damage anything if it just slipped off of the shifting fork or pin or whatever that is called. I just would like to know what it could possibly be that is causing this before someone tries to drop my transmission and CV axle to get to whatever they think it is. That's a lot of work for an assumption. So I just wanted to know everything it could be to try and start small and work my way up to the big jobs if need be. It's my first car so I don't have a lot of cash to throw around on all these assumptions by people who want to call themselves mechanics with 5,000 cars sitting in their yards. Please and thank you.