step by step smps
Well, then you should start with the buck regulator and understand how it works. Especially that you have a chip to play with.
Once you've done that, you can try a forward, which is a buck-derived topology, but uses a transformer for isolation.
Then you can try the boost and later the flyback, which is boost-derived, but again uses a transformer.
Once you know these basic things, you can build almost anything you want. The only differences will voltages and currents