In the directory containing the tsh.c file, create an etags index:

 etags tsh.c      
   

This will create a file named TAGS. You only need to do this once.

In emacs, search for a tag by typing M-. (Alt plus the "." or if that doesn't work, the ESC key and "."

Then at the mini-prompt area at the bottom of the emacs window, type the full name or a prefix of

• global variable
• function name
• preprocessor defined symbol (e.g. #define MAXARGS)