To make bookmarking simple, I would recommend adding one of the bookmarklets. You can view the bookmarklet options here. New users are recommended to use the "diigolet". Diigolet is added to your bookmarks bar by a simple drag and drop.
Once it is added, click on it and the image/options below will appear.
One more click -- on bookmark --and you will be ready to enter information to save your bookmark.
Often the Url and Title are filled in for you. Double check the title to make sure it is clear. In the image to the right it says "My Library", changing it to say "My Diigo Library" would help clarify.
The description section should express why you saved the site or provide a good description of the site.