On your Themes page there are only a couple of things you can do short of activating and customizing your themes. At the top of the page, as seen in the below image, you can either Add a new theme or if you happen to have many installed themes, you can search for them by name in the Search bar.

Frankly I doubt anyone would be using the Search bar feature, mainly because hardly anyone would have so many themes installed on their website. Even I with my test website only have 8 installed themes. Also on the Themes page there will be an area with a big + sign, see below image, which is an alternate area for adding another theme.

Pretty easy stuff to understand so far, and now it is time for you to understand how to select from more than 2,100 theme templates as well as how to refine your search for your new theme selection.