Whatis looks up a given command and gives the header line from the manual section. You can then run the
man(1) command to get more information. If the line starts `name(section) ...' you can do `man section name'
to get the documentation for it. Try `whatis ed' and then you should do `man 1 ed' to get the manual.
Whatis is actually just the -f option to the man(1) command.