Do you want a list of all the known cats in the world (or at least, the ones that have Wikidata items about them)? Click on the Examples button and have a look at the first example - Cats.
In a minute when you click on the word Cats, it will open the query and allow you to run it. Clicking on the pencil icon lets you edit the query. The camera icon lets you preview the results of the query. And the eye icon lets you preview the code.
Now click on the word Cats to get started. Then click on the blue arrow in the lower left to run the query.
Your results consist of two columns: one column labeled item which consists of Wikidata items (wd:Q28114532, for example) and the other labeled itemLabel which lists the label associated with each item. Recall that item labels are what make Wikidata items interpretable to humans.