To create the graphical elements of your 2D games with DirectX all you need is to know how to load textures, display text and use the D3DX sprite interfaces. Links to the pages for these topics are below:
Another part of the DirectX SDK that is useful is the DirectInput API, it allows you to take input from the keyboard, mouse and other devices. Notes on DirectInput can be found here:
2D Games with DirectX Techniques Index
Once you can display sprites and handle input you are ready to start creating your 2D game. Please follow the links below for the various techniques:
I will add many more techniques to this site in the near future.