Adding icons to the Dock
From Mac Guides
Applications, documents and folders can be added to the Dock to make it better suit your needs.
To add an item, simply drag its icon onto the Dock. Applications can only be added to the left/top side (that is, to the left/top of the separator on the right/bottom side of the Dock), while documents and folders can only be added to the right/bottom side (along with the Trash and minimized windows).
The icon for a currently running program can be told to persist in the Dock by right clicking on the icon and choosing "Keep In Dock".