See how to reassemble a P08 Luger pistol (also known as Pistol Parabellum) after a field strip. Then you're all ready to insert that magazine into your gun for a proper weapons check.
Be sure to follow all disassembly and assembly instruction found in the technical section of http://www.lugerforum.com.
If you are not sure of what you are doing or if the gun is not working properly, take it to a competent gunsmith.
Be sure to follow all NRA firearms safety recommendations.