Welcome Frank. Please
read the rules so you know what to do and what not to do.
Try /usr/bin/which or /usr/sbin/which instead of just which (I would guess it isn't built-in as they stated in your book).
% /usr/bin/which w
If the cursor becomes a > sign, then it was usually because a full command line wasn't typed - and it's waiting for you to finish the command sequence. Pushing the Control key and C at the same time should get you out of it.
Use the man pages for assistance also. They are sometimes hard to understand, but no one said it would be easy!
% man which
If you can't get these examples to work, look at the PATH variable and MANPATH variable
% env | more
env will give you all the environment variables, | is the pipe sign, and more is to let you look at it all a screen at a time.