How i know that file i include in this directive?

eg.: if a go to use MessageBeep, what directive i'll include? How i know it?

in your imports section under User32.dll add messagebeep to the list of api included. then you can call it normaly

If you got the win32 programmer's reference file, you can find the import library for all the api calls by clicking quick info.

...may be I stumbled over a similar problem...

I tried to get some function that returns the height and width of the current screen setting. The Win32 programmer manual offers a function called:

int GetScreenHeight(void);
int GetScreenWidth(void);

...but I can't find out to which .dll it belongs, adding the lines in user32.inc only resulted in something like 'function not found in user32.dll') ...how can I use this or similar function with FASM ?

After some searching I can answer my question myself

invoke GetSystemMetrics,0 (-> Screen Width)
invoke GetSystemMetrics,1 (-> Screen Height)

from user32 does the job perfectly.