If you launch an app from Launchpad or from the Applications folder in OS X, and that app isn’t already located in your dock, the app will disappear from the dock upon closing it. That’s the desirable result for apps that you run occasionally, but for apps that you launch and run all of the time, it may be best to keep that app as a permanent fixture in the dock.
There are two basic ways that I like to go about keeping often-used apps in the dock. The first way is to simply right-click on the app icon in the dock → Options → and select Keep in Dock. Once you do this, the app will stay permanently affixed in the dock, even if you close the app.
The second way to keep an app in the dock is to move it to another place in the dock. Moving an app in the dock indicates to OS X that you want to keep the app in the dock, otherwise you wouldn’t have bothered moving it in the first place. When you move an app in the dock, the Keep in Dock option is automatically checked.
If you ever want to remove an app from the dock, just right-click on the app icon in the dock → Options → and deselect Keep in Dock if the app is running. Upon closing the app, it will disappear from the dock. You can also simple drag and hold a non-running app outside of the dock to make it disappear, or right-click on the app icon in the dock → Options → and select Remove From Dock if the app isn’t running.
I understand that this may be old news to seasoned Mac veterans, but since the Mac has been selling so well as of late, there are bound to be lots of newbies that haven’t fully grasped how the Dock works on OS X. Please sound off in the comments section if you have anything additional to add to help fellow readers.