To buy parts on RacingJunk.com, click on the part you are interested, and then click the Buy Now icon. This directs you to the part owner's website where it can be purchased online.
RacingJunk.com does not take payments on its own, as it functions as an advertisement site. The site lets users browse different categories of parts available or use the basic search function. Click the appropriate button and it leads to the website selling that part. Find the part on the seller's website and use its payment system. Most sites take major credit card payments, though some might also take other payments, such as Paypal.