Play: When this button (i.e, ►) is clicked, it will execute the query or mutation in the left panel.

You can add labels so that you may enter multiple functions. Labels are given immediately after the text query or mutation. You can see examples of this in the screenshot here: all_repos and one_repo. With labels, when you click on the Play button, a box of your choices will appear (see screenshot). You would then click on the one you want to execute and its results should appear in the right panel.

Prettify: This button (i.e., an icon of a broom) will reformat the query or mutation to a make it more easily readable. It will add hard-returns, indent text and may remove extra spaces. This has no effect on the results, though.

Merge: Use this button (i.e., an icon of an X encased in square-brackets) to merge two queries or mutations when you're using fragments within to store individual elements. Merging them replaces the original named fragment with in a given function.

Copy: This simply copies the current query or mutation to the clipboard. You can then paste it into your code using whatever text editor you're using.