PaidToClick - PaidToRead

PTC stands for Paid To Click, while PTR stands for Paid to Read. At PTC / PTR sites you get paid to click on ads and visit websites (PTC) or to read email in your inbox or drectly in the site(PTR).
Those kind of site pays an amount ranging from $0.005 to $0.01 for each website you view and an equivalent amount (sometimes a little lower) for each website your referrals view (you can refer people and gain some money for every click they do).
The original purpose of PTC was (or better should have been) to boost traffic for sites needing to advertise their products or services, like small e-stores and other advertising firms. So the advertiser pays some money to show their ads and the members receive part of this money to view those ads (and maybe buiyng some of the advertiser's products).
Simple, isn't it ? Unfortunately in my opinion at the moment a small number of those Sites offers this kind of service, having the remaining a totally different aim: to drain money from members. That's why almost all PTC sell bots referrals (that means not human referrals, but part of software code simulating human referral activity, in a word: clicking on the ads).
Why PTCs sell bots? To gain more money, obviously. The Drawback is that no one advertiser is eager to invest his money in ads when there is no people to look at, but only a bunch of code rows in the site script... bots don't buy products. That's why if you linger to look the running ads of any PTC sites there are few REAL ads, the great mayority being self referencing ads, or ads promoting other PTC sites... few ads promoting REAL business or Products.
Sites offering an excessively high click rate and selling bots are using a model non sustainable in the medium-long term. That's why the promised high returns aren't obtained by revenues generated by any real business, but out of the money paid in by other members. Such kind of model, called Ponzi Scheme, is destined to collapse as soon the money paid from new members are no more sufficient to pays the promised returns. That's why you have to approach PTC business with extreme caution, and don' invest in PTCs money that you are not prepared or that you can't afford to loose.