see the sidebar. click from there the "add bookmark" and you see the attached screen. click "all tabs" - when you have a collection of links you want in one click. you can later open them singularly as well.
To answer the second part of your question, you can set whether Camino opens links that would normally open in a new window in a tab instead by going to Camino > Preferences > Navigation > Tabbed Browsing.
There you'll find an option for "Clicking a link with the (Command) key down:
Opens a new window
Opens a new tab
Note that whichever one you DON'T select is the default behavior.