Go up to the top Spotlight search (on the right on the mac desktop) and type in Motion. Launch it, and when its running right click on the dock icon and choose "keep in dock". Then slide the icon left or right to put it in the slot you want.
Great advice Frank.
If you drag the icon off of your dock it will explode aka delete itself, it can happen by accident every once in a while. If you upset I find exploding your icons can be quite relaxing.