set path = ( $path /usr/local/bin ) or whatever directory you wanna add. oh yea dont forget to rehash after you used this command.
Also if you want to make it permanent add it to your /.tcshrc file. Just open it (vi ~/.tcshrc or any other editor) then add the set path line, save the file, and rehash or open another terminal window. (this is for tcsh shell only for bash or sh it would be slightly diffrent)