The little icons in your system tray, located in the bottom right-hand corner of your screen each represent a task that loads up every time you boot up and runs in the background. Hover your mouse over each icon to display the program’s name. Click on the button that has the < arrow to show any hidden icons. Some of them belong here, such as the battery power icon and the network status icons. Many of those little "quick access" icons, however, take up quite a bit of room and increase boot time.
Some of these processes can easily be disabled simply by right-clicking on the icon, which will open a pop-up with the option to disable it so it will not start up again. However, some only give you the option to stop it from displaying, but continue to run anyway. For these, you will use one of the two methods detailed above.