One of the funny things about the Graphical User Interface is that while the interface is graphical, the help files are textual. So if you were new to word processing and didn't know the English word for italics, how would you look it up in a help file? It's impossible! The same thing happens with that little area to the right of the Start button.
It turns out that this area is called the Quick Launch area. The operating system decides which icons to put in the Quick Launch area by looking in a specific directory named:
C:\WINDOWS\Application Data\Microsoft\Internet Explorer \Quick Launch
If you look in that directory, you will find that it contains one entry for each icon that appears on the screen. In your case, since you have three icons, there will be three entries in that directory. The following three approaches are the easiest ways to add more icons: