Start with basic pong. You'll learn a lot from just that.
Then add to it.
Things you'll hopefully learn from pong are,
- Timer based movement
- Collision
- Vectors (possibly)
- Object creation and movement
- Sprite creation and movement
- Scoring
There's more, but you get the idea. A very simple game can get complex pretty quickly.
You probably don't need to "buy" anything else at the moment. Almost everyone will recommend you get Sparky's Collision DLL which is free. There are several other free DLL add-ons too that cover many of the things you might need for just about any game project.
Dig in and throw pong together and see what happens.