Login Items will be automatically launched on startup. See Set Startup Items for Mac for more information.
Adding login items can be performed using the plus button inside Accounts Pane. However, this way is slower than other way, i.e. Dropping Icon. By dropping icon, you can easily and instantly add login items to your Mac.
There are three most common ways to search for icons to be dragged into Accounts Pane.
Drilling deep into Finder, folder by folder, will slowly bring you to your desired icons. Usually, Applications will be put inside Applications Folder, which is located at Macintosh HD → Applications.
Icons are implicitly inside Quicksilver. In simple way of saying, Quicksilver calls up the icons. However, it’s a bit hard to use Quicksilver to call icons except Applications’ icon. Keystrokes Option-Space can be used to invoke Quicksilver.
Spotlight must be very familiar to Mac user. Searching results of Spotlight Pane can be considered icons. Spotlight Pane can be opened using keystrokes Command-Option-Space.