I want to be a emacs user, but when I follow the tutorial, I am always lost-_-.

1, How to using "Multi-file searching". this is copyed from the tutorial
Create a TAGS file for the files of the given program, as described in the previous section. Place point at the function name for which you would like to see the definition and press M-. (find-tag)
So I use etags *.java to create a TAGS file, then do what tutorial asks me to do, then I get nothing!!!!!! I think I must miss something, but don't know how to overcome it.

BTW, I am still comfused about the creating a C file index is to use the command "etags *.c", where is the head file????

2, I am totally lost when I try to learn the procedure of "Finding differences between files"? what should I do at the very first step????

What is wrong with me? Can anyone give me a hand? Thanks in advance.