Alright, lets make this simple.
See, theres this thing called a mouse see, and you take it in your hands. Now you place that mouse on a mousepad. Now we move the mouse so the little arrow thing on your screen is over a part on the desktop. Got that? ok. Now, theres two buttons on the mouse, a right one and left one. You want to push the right button now. Now we see a menu. You'll want to push your little arrow over to the "Keep Aligned" option. Now with the arrow still over that, push the left mouse button this time. Now, the icons are aligned. Yay!
summary (for advanced users only): Right click on the desktop and select the "Keep Aligned" option.