There are many newer blocks that don't have help dialogues yet. I've figured most of them, but some are still mysterious: like define (block) [ ] and the new sound and new costume blocks.
Also, some help dialogues need updating, like [ ] to [ ].
New Snap! users will often look at the help dialogues but will be disappointed when they find that these blocks don't have a dialogue. Some are easy to figure out, but others like those mentioned in the first paragraph and blocks such as cut from and paste on.
There is someone, I can't remember who, that is (or was, idk if they're still doing it) creating the missing help menus. Of course, they are working on a new help dialog system, which is so much better. I have no idea when that'll be finished (it started a 1-2 years ago, or maybe even longer).
It's like a function with normal text-based programming languages. You define a function by its name and by any arguments you'd like to put in it. And if you don't know what an argument is, don't worry. All an argument is is just a variable and a value.
I don't know how to explain it. But I'm pretty sure anyone can explain it better than me.
i'd reccomend krita, the ui is a bit more complex but it can do just about as much (slightly slower in a few areas, very fast and powerful for drawing) and isn't too hard to learn
it's what i've always used after switching to linux