To set a filter, simply click on the filter icon on the right above the table/list. You'll be able to create new filters or load a saved filter.
Depending on whether you are in the project, customer or user overview, you will be provided with different filter options.
When creating a new filter, enter a name for the filter in the filter selection field on the left (the red text means that the filter is unsaved) and click on the save icon on the right.
☝️ Note: By the way, the filters in the Project Overview are the same ones you'll be able to select or create on the Dashboard for the Projects widget. Changing the filter will also affect the other view.