u/Educational_Push9319

Hi, first time poster and complete bike repair newbie. I am struggling with even understanding what the issue is here and would really appreciate help with knowing what I'm trying to fix. I've been searching various things about derailleurs and confusing myself!

I have friction shifters and during a ride the rear gear just stopped shifting, it was tight and wouldn't move. When I got home I can see that the derailleur is hanging in a forwards position. I can push it back into place but it doesn't stay there.

What's happening here?