See the UNIX Programmers Manual or via % man csh
% pushd dirname will cause the current working directory to be remembered, and then cause the dirname to be the current working directory. To revert to the original directory, use popd.
% pushd with no arguments will swap the present directory with the next entry in the directory stack (see "dirs"). This allows alternating between two directories with a minimum of keystrokes by repetitively typing "pushd".