Going from basically no coding experience, it took me a couple of months to really start getting the hang of Petit Computer (the predecessor to SmileBasic). A big thing that helped was the help menu, something which was vastly improved in SmileBasic. So long as you're willing to test out new commands and combine them with others, it shouldn't be too difficult.
It varies. The basic concepts are readily understood. Some of the advanced concepts, such as Sprites, backgrounds, animation, and music, take a while to understand.
