Blueprint Question - Functions, Events and blueprint class

there is any documentation that explain what blueprint class is better for “what”?
also i have a little problem, i want to create functions with the blueprint function library, but the LE HTTP blueprint node ask for an “On Complete” Event, and also if i create the function for it with the same PIN the dropbox is always to NONE, elsewhere is working correctly, so my anser is:
There is anyway to use the Blueprint function library with Events or there is any place where i can create my logic function accesible from everywhere? (i’m talking about login, registration, inventory update, and any functions that communicate with my PHP library)


Game mode is acessible from anywhere, bu i do not remember if its server only or on every client in multiplayer.
There was some diagram of how all those base classes are connected, but i cannot find it atm.

I found some stuff about it:

iIt looks like you want to use game state for storing such info.

Thanks Nawrot, your answer helped me.