On the Set texts page, you can fill in a few texts that will be shown in the interface and around the publications. For every text, there is a title and explanation of the location of the text.
The texts are split into these sections: search engine texts, general texts interface, buttons & popups, log in. If some of these features are not available in your interface you don't have to fill in the texts of course.
If you have publications in multiple languages you will see tabs switch to other languages.