Hi Stevo
Assuming you live in the modern world where having kids before married is perfectly acceptable, there are a few things you can do to make your girlfriend pregnant.
1st - check she wants to be pregnant!
then stop using contraception, no pill, no condoms etc.
If it does not happen naturally, you can buy a fertility kit which will allow your girlfriend to monitor when she is most fertile in the month.
If this does not work, go to the doctor and check your little swimmers are OK and she is all OK.
One tip for guys trying to have kids - try to avoid tight underwear - boxers allow the optimum temperature for the little guys!
Good luck!