If you are missing icons in your dock, or you want to add Applications to your dock, follow these three steps:
1. Make sure you are in the Finder. You can get to the Finder by clicking on the Finder face icon (furthest icon to the left) in the dock or by clicking somewhere on your background. You know you are in the Finder when you see "Finder" in the menu bar at the top-left corner of the screen.
2. Once you are in the Finder, click on the "Go" menu at the top, and choose Applications.
3. You will now see a list of all the Applications on your computer. Find an Application that is not currently in your dock. Click and hold onto the icon and drag it down to the dock where you would like to place it. The icons located in that space should spread out and then you can let go and the icon should stay in your dock.