It's actually a pretty simple subject.

A dream guide is your guide through your dream (makes sense ) and can tell you (hopefully) how to move on in your dream, how to take care of things and sometimes even what to do about something in your life. What's wonderful is that you'll never know how your dreamguide looks. To see him in a lucid, just simply summon him/her/it like you would do with any other object. That's about it!

Popular questions are:

Who are you
Why am I here
What should I do