I think it is simpler.

The event can CALL another function. Say you got a function in Module1 then you can call it by

call module1.myFunctionABC() if it is a sub or

if the return type is a string

MyABCStr = module1.myFunctionABC()

One can leave the module1 part as the editor will recognize it, but if you have a bigger project I like to include it. Its a personal preference.

Explination in code 
private sub btnABC_onclick() 

 call module1.myfunctionABC()

end sub
In module1 
sub myfunctionABC()
  'Your code
end sub