where can I find manual for craft forms there is tool forms(/craft/app/templates/_includes/). But I cannot find usage manual, ex. options for forms.select etc. Where is it, guys? Thank you
At this time, there is no manual for it.

It's an incredibly useful chunk of code, but it's buried pretty deep in the system. I think the belief is that "if you're capable of finding it, you're capable of backwards-engineering it."

I'd actually suggest looking to other parts of Craft (and other plugins) to gain a better understanding of some real-world applications and examples.