Insert the tip from the PEX around the end from the fitting. Slide the end on the PEX tubing which has the crimp ring or cinch clamp on it about the tip from the fitting that you choose to screwed onto the copper tubing. Drive it on as far as https://andreskwdim.anchor-blog.com/11204790/the-definitive-guide-to-1-2-copper-street-90