First, why would you want to use the Filter View?
The Filter View gives you an alternate way to view a set of Tasks that all meet certain criteria. In the Filter View, you can choose to filter Tasks by Tags that you can assign or by dates.
For example, if you want to only show items that you need to get when you’re out doing errands, assign those tasks a tag (for example, Grocery store or Home Depot). Then, when you’re about to go to Home Depot you can pull up a list of just those tasks in the Filter View.
The Filter View also has built in functionality that allow you to see Tasks due today, overdue Tasks, and upcoming Tasks. Or you can show all tasks that have due dates, in order from oldest to newest (in Filter View show “Tasks by Due Date”)
Second, HOW do you use Filter View?
To access the Filter View on the Mac or PC, click the button three vertical bars on the right side of the titlebar area. This button is used to toggle the Filter View on and off. Then tap on the filter icon on the upper right to choose which filter you want use.
Filter View on iPhone an iPad is the 3rd tab at the bottom of the app. Select that option called Filter View and then choose the filter you want to use.
See: How do I use Tags?