You may notice that at the top of the first panel that it has a tab and that there's a plus-sign to the right of it. You can click on that plus-sign to add another tab, another left panel for entering more queries and mutations. This can be an alternative to using labels — or you can do both, use labels and use multiple tabs.

At the bottom of the page, below the left panel, clicking on Query Variables and Request Headers opens two bottom panels. They will allow you to customize the variables and request headers used for a request.