Think of all the questions you may be asked and then practice your answers. Have student's practice entering a URL in the location box. Have student's practice traveling by clicking links. Have students conduct a search using a directory. Try the easiest way first.
People remember stories and examples much longer than an hour lecture on theory.
Then tell the students what they will be able to do. Conclude with a summary of your major lessons of the day. Have a good time. If you do, your group will also. Attend library classes or tutoring.