So, I see you want to learn how to use MML to create music. I'm not the best at SmileBASIC, but I can help you with MML
So there are 7 types of notes (from lowest to highest): C, D, E, F, G, A, B. You can also choose how much time there is between 2 notes, 1 being the most time (I don't know the least time).
So let's say you made some music, you use BGMPLAY to play that music, and BGMSET or BGMSETD to set the music (I personally use BGMSET the most)
An example of some music that can be played is: BGMSET 128,"@001C5D5E5F5G5A5B5A5G5F5E5D5C"
BGMPLAY 128, this would work, but the music would play once, then finish, to keep on playing the music, you put: BGMSET 128,"[@001C5D5E5F5G5A5B5A5G5F5E5D5C]"
BGMPLAY 128. If you want to change the instrument, go to the SMILE tool, click GM and get your instrument there, to insert it put @(that instruments number)