tkdiff <file1> <file2> to compare two files.
tkdiff -conflict <file> to merge a file with conflict markers generated by "merge" or "cvs", The file is split into two temporary files which you can then merge as usual.
tkdiff <file> to compare <file> with the most recent version checked into CVS/SCCS/RCS (checked for in that order).
tkdiff -r <file> to compare <file> with the most recent version checked in.
tkdiff -r<rev> <file> to compare <file> with revision <rev> of <file>.
tkdiff -r<rev> -r <file> to compare revision <rev> of <file> with the most recent version checked in.
tkdiff -r<rev1> -r<rev2> <file> to compare revisions <rev1> and <rev2> of <file>.