The dash is where you can put links to all of your favorite applications for easy-access. To add an application to the dash:
Open the activities overview by moving your mouse pointer to the top-left of the screen.
Find the application you want to add to the dock, right-click it and select
Alternately, you can click-and-drag the icon into the dock.
To remove an application icon from the dash, right click on the application icon and select