Instructions
Go to Google's Looker Studio and open the Looker Studio Report you are working with
Click the Edit button:

Click on the table you would like to apply a filter to
In the Chart column, locate and click + Add a Filter:

Select Create a Filter:

Create your filters to include or exclude certain dimensions. You can also select from many operators to determine the content that is shown in the filtered table:

Note:
In the example image we want to show Page Titles that contain the term News Flash.