Once you have set the filters and columns to show, you can run the query by click on the blue "View Results" button. The results will appear in a table below that button.
To export the results to CSV, click on the "Export" button as shown above, or select "Export" from the "Actions" menu.
The "Actions" menu contains actions you can do on the resulting data. You do not need to run the query by clicking on "View Results" before executing any of these actions.
Please see other help articles for details on how each action works.
You can click on the "Reset" button to reset every back and construct a new query. The default query is shown below. This is the same view you get when you first visit the query builder.