Make the Finder sidebar and toolbar yours

The Finder is the Mac’s file manager, and its defaults assume you use the folders Apple ships rather than yours.

Sidebar. Drag any folder from a Finder window onto the sidebar and it stays there. To remove something, right-click it and choose Remove from Sidebar — that only takes it off the list, it does not delete anything. For the built-in entries, Finder → Settings → Sidebar has a checkbox for each.

Toolbar. Right-click the toolbar at the top and choose Customise Toolbar. A sheet drops down with every available button and you drag them in or out. AirDrop is a good one to add: select a file, click the button, and it is on your phone. New Folder and Delete save a trip to the menus.

One more worth turning on, in Finder → Settings → Advanced: Show all filename extensions. Without it the Finder hides .pdf and .jpg, which is confusing if you are used to seeing them.