During the installation process, many Mac applications will ask if you want to configure them to launch automatically when you start your Mac. †The truth is, you can configure any app to start automatically when you boot your Mac. You can also set document windows to open automatically, or configure network drives to automatically mount on the Desktop.
Screen shot courtesy of Coyote Moon Inc.
For example, I've set my user account to automatically launch the following apps: Meteorologist, Activity Monitor, Messages, Stickies, and a few others. I've also configured a couple of network volumes to mount on the Desktop whenever I log in to my Mac.
To accomplish these feats, all you need to do is fiddle around a bit with the Accounts preference pane or the Users & Groups preference pane, depending on which version of OS X you're using. In either case, the method of adding login items is the same.
If you would like to automate the process of launching apps or mounting drives, take a look at our guide: