This applies to Windows Explorer in Windows 10
Pin
If you want a folder to show up in Quick access, right-click the folder and select Pin to Quick access. Unpin it when you don’t need it there anymore.
Remove
If something shows up in Quick access that you don’t want to see there again, right-click it and select Remove from Quick access. It won’t show up there anymore, even if you use it every day.
Show Only Pinned Folders
To turn off recent files or frequent folders, go to the View tab, and then select Options. In the Privacy section, clear the check boxes and select Apply. Now Quick access will only show your pinned folders. (If you turn them back on, items you previously removed from Quick access might show up again.)
Open to This PC
If you’d rather have File Explorer open to This PC, go to the View tab and then select Options. In the Open File Explorer to list, select This PC, and then Apply.