If you have a favorite web page and you would like to revisit it many times, then it isn't fun typing the URL of the web page every time. The Browse Activity can store URLs for you - each URL you store is called a bookmark and they stay stored even if you switch the computer off.
Now I want to save a reference to this web page so I can easily visit it later. I do this by clicking the star next to the Location Bar. When I do this a small colored square is added to the bottom of the Browse Activity and it has a picture of the web site in it.
I can store as many bookmarks as I like. Then when I wish to visit a bookmarked web page I click the associated square at the bottom.