There are 2 ways to add another report tab to the report you are working on.
The Plus Button
The first is to use the + button in the top right corner of the report window.
The Current Report Tab
While working in the current report tab, select the arrow drop down of the report tab and select "+New"
Now there will be two tabs, Report 1 and Report 2. Click on a tab down arrow to select rename it to name it something more useful.
Please note that Report 2 is blank by default.
Click the Templates tab on the left and drag and drop a Table onto the report. Then, click on the Data tab on the left and drag and drop fields as needed.