Phase 1
First thing to do when you decide to start earning with PTC sites is to make an account on one of the available payment processor. That is most likely to be Alertpay.
When registering be sure that the information that you are asked to give is correct.
Phase 2
Next step is to join PTC sites.
The sign up process is very easy. You will need to choose a username, password, email address, alertpay email address for payments (my advice is to use the same email address because it may take a little longer to process the payment if they are different), select your country and you are finished.
As I metioned in Tips, DO NOT be lazy to read their TOS (Terms of Service) or to go through their forums and read posts from other members before joining. This is the best way to protect yourself from being scammed as many new and old PTC sites tend to be scams.
The list of PTC sites on the Home Page is tested so you can start with signing up there.