Here the sample how to use global variables for other forms.
DataModule : dmDataModule
public
{ Public declarations }
fMyGlobalVar_Userid : string;
published
property MyGlobalVar_Userid: string read fMyGlobalVar_Userid write fMyGlobalVar_Userid;
end;
Form1 :
var
UserId : string;
begin
dmDataModule.MyGlobalVar_Userid := UserId;
end;
Form2 :
unimLabel1.Text := dmAppModule.MyGlobalVar_Userid;