You should start by reading the official e-manual...
http://smilebasic.com/en/e-manual/manual11
You should also read the electronic manual bundled with the game by starting the game, pressing Home and selecting Manual.
Afterwards, you can play around with various instructions and slowly start to get programming experience.
Most programming languages I've learned (or tried to XD ) start with core functions like "do", "for", "goto". Try looking for some of these basic functions and it's use on the electronic manual, the in-game tips or even google. It's a good place to start trying to understand how these work.
Then you might like to move onto other, more game-programming oriented functions like those who handle sprites, animations, backgrounds... you'll find out that making an animation loop requires a programming loop like those you'll see when learning dos and fors. Then, ideas will start popping out of your mind as you program. You should try them...
And also (and very important) you should not let be overwhelmed by those big, big unbreakable diamond walls you'll find while programming. If so, let the program down for a while and try to come back to it with a fresh mind.
