Cowebs are a new concept for a lot of people. Basically they are just a collection of pages that everyone can edit from the web browser.
Here are the basic things you need to know:
1. You need to be logged in to edit pages.
2. Clicking the 'edit' link will edit the page you are currently viewing.
3. Simply type text to define the page, no HTML is required (though it can be used).
4. The format of your text is preserved unless you start using HTML tables and such.
5. Enclosing the name of another coweb page in double square brackets will create a link to that page.
6. A good way to see how a page was made is to click 'edit' on that page, look at the text, then click 'cancel' in the edit form. Try it on this page if you want.
Also see the discription of creating pages over in the Coweb on Cowebs: http://www.nthlab.com/coweb/cowebs.php?key=Creating+Pages