All the files in your Incoming directory (~/.aMule/Incoming, by default) are automatically shared. You can change the IncomingDir key in your amule.conf to use a different directory.
Other shared directories are named in ~/.aMule/shareddir.dat. One directory pathname per line, absolute and including the trailing slash ('/'). Subdirectories of the named directories are not automatically shared. If you want a whole directory hierarchy to be shared, you have to put each (sub)directory's pathname in the file.
