What part of "by works a man is justified; and not by faith only" do you not understand?
None of it. I understand it perfectly because I understand the whole counsel of Scripture and the harmony of Paul and James. SHOW ME YOUR FAITH without your works and I will SHOW YOU my faith By my works. Works is evidence. It is not the cause of salvation. When one claims to have faith but doesn't have works then he is not justified in that claim. When one claims to have faith and shows good works, then he is justified in that claim because true faith is a faith that will work.
Salvation is NOT OF WORKS. But it works. Capisce?