How do I add my own keywords to my images?

You add keywords to your images by going to the Content Administration view in your image bank.
Click on "Images" in the left menu, open a collection, and then click on an image to open the side panel where you can add and edit keywords and descriptions. 

Click on "edit" and start typing a keyword. You separate the keywords either by adding a comma between the words or by clicking enter. Don't forget to click on "save" once you're done to make sure the keywords stick.