Usually, the primary project file is called main.agc, but perhaps you have changed it to cards.agc.
In this primary file at the top, write the following line:
#include "Functions_Lib.agc"
This is a relative path, relative the the project AppGameKit file (which should be in the same folder as main.agc / cards.agc). So if you have created an includes subfolder (like I do) then use:
#include "includes\Functions_Lib.agc"
When compiling, AppGameKit treats this as one big file. So all of your functions will be called correctly, you don't need to do anything special.
Quote: "it has been a bit confusing attempting to adjust from DBPro"
This feeling is temporary, in a week or so you will speak fluent AppGameKit!
Quidquid latine dictum sit, altum sonatur