It's easy — just click the star!
To create a bookmark, click the star icon in the address bar. The star will turn yellow and a bookmark for the page you're on will be created in the Unsorted Bookmarks folder. That's it!
Tip: Want to bookmark all of your open tabs at once? Right-click on any of the tabs and select Bookmark All Tabs... from the context menu. Give the new bookmarks folder a name and choose which folder to store it in. Click Add Bookmarks to finish.