To do this, first click the “Accounts” icon in System Preferences. With your account selected in the sidebar, click “Login Items” at the top of the main pane. You’ll see a lit of items that will open automatically when you first log in; items with a check to the left of them will begin hidden and out of view.

Add a new application to the list by clicking the plus sign below the list. You’ll then get a Finder window in which you can choose the application you want; once selected, click the “Add” button. Then click the checkbox if you want the application to begin hidden.

You can also add things other than Applications. Select a file or folder to have it automatically open when your Mac starts; choose a song or video if you’d like to see that.