How blueprint function was created?

i want to create blueprint function like function exist in blueprint database. what i need to know how it created? what need to know to create blueprint function? api? is i should learn about api? how blueprint work?

Didn’t quite understand what do you mean.

Do you want to have some common blueprint functions? In that case you can create a blueprint function library in blueprints, consisting of only functions, which will be accessible everywhere in the project blueprints.

Or do you want to expose some C++ code to blueprints? In that case create a C++ class, inherited from Blueprint Function Library Docs