What is the best way to create a guest account for our site?

1) Click Manage Classmates
2) Click the Enter/Edit Classmates button
3) Click the Add New Member button
4) When creating the new member, mark that the new member is either a Guest, or a Non Display Guest. Right there on the page where you're specifying if the member is a Classmate, Guest, or Non Displaying Guest, there is a help link you can click on that will give you full details about what each account type is and how to use them.