The acronym PTR means Paid To Read and, even if seems strange, you have to do only one thing to see your money credited: open the mails and click on the link. That's all.
After you have waited for some time (10-60 seconds, it changes from site to site), you'll be paid for your "hard" work.
Usually in the mails there are other site ads or, more often, link to search engines. To learn something more about this fact (and about the importance of the valid searches), I suggest you to take a look to the FAQ.