You can just drag and drop items directly into the list to add them. It’s usually easier to just drag and drop though. To add a new application into the startup list, you can just drag and drop the icon into the list, or you can click the Plus icon and select an item using the file browser manually.
Removing items is as easy as selecting one and clicking the Minus button. You can select an item in the list and click the Minus button to remove it from starting up, and you can check the Hide box to make the application not come to the foreground when it starts - it’ll basically start up, but minimize itself into the dock when it starts. Now you’ll see a list of items that will open automatically when you log in. Once there, find your user account on the left-hand side (although it will always be selected), and then click on the Login Items tab. Open up System Preferences, and then click on the Users & Groups icon.
