What is this in blueprint?

I chose Unreal Engine because of good documentation:

you have everything here

what is variable, function, override, function, macro, graph, even dispatcher?

Yes, looking over the docs is where you might want to start. As well as some videos, found by using a quick and simple tool: Google + YouTube:

what different between event graph and function graph? what is macro? i use event graph for what? use function graph for what?

The event graph is where events get fired, so “Event BeginPlay” for example. In this graph, you can call FUNCTIONS you have made. The function graph is where you build up functionality, for a given function you have created.

For example, let’s say you make a function called “PrintName”. In this function, you just print a simple string. Now, in the event graph, you call that function from the “Event Tick”.

So, function graph is the drawing board for your functions. The event graph is the drawing board where events get fired, such as Event BeginPlay, Event Tick, etc.