CnC:
First : the walk was a little weird cause he didn't really bend his knees .
Second : It is jittery, though for your first animating that's pretty good . Things to stop that would be better construction and not sure if you did but double framing would help too ( I'm new at this too so tell me if i'm wrong ). A tutorial on that and how and when to use it: https://www.youtube.com/watch?v=LfMEswULqpU .