Pay to Click sites typically involve visiting a number of ad sites each day for which you get paid extremely small amounts of money. If you can refer others, then it is possible to increase your earnings by a considerable amount because you also get a share of the earnings from their clicks.
Some, but not all sites allow you to rent referrals. There is, of course a risk that you will rent someone who is not active and the sites can't guarantee that any member you rent will be active. For a sum smaller than the original rental fee, you are usually allowed to exchange your inactive member for another one.
There are some sites which you will see advertised a lot, but are not necessarily reliable. Neobux for example has had bad ratings in the past for being slow to pay and for slashing the payouts to free members after they have already done the clicks and earned the money. That's what happened to me in the past. They may have improved, but I am not wasting my time going back to find out.
Other sites have a very high reliability rating and have a fair number of ads to click every day, whether or not you are upgraded. Clixsense is one of these. In addition to the straight ad clicks, you will find the 'Clixgrid' where you can find cash prizes under some of the squares and also surveys and offers. On the plus side, the Clixsenseupgrade is only $17 for a full year, on the downside, they don't rent referrals.
Wordlinx is also worth a look although they don't have a lot of ads every day. I have also joined Clixten who seem to have a good number of ads per day, and you can also earn by watching short videos.
My top recommendation for the moment is Nerdbux. If you are a member of the Sweeva traffic exchange, ClickTrackProfit or Trck.me, you will already know that their admin is reliable and trustworthy and Nerdbux is another site from the same team.
There are loads of ads every day - up to 60 or even more, they rent referrals at competitive rates and there are other options for earning money. Offers, the Nerdgrid (like CLixgrid) and micro jobs.
Now you may think that clicking a load of ads every day for a tiny return is not worthwhile. This is the strategy I recommend you use for Nerdbux. Rent referrals as soon as you can from your earnings and you will find that your income snowballs very quickly. You can rent one at a time. Don't put a big sum in to rent referrals as you will spend all your time recycling the inactive ones and waste your income.
Grow your referral team one or two at a time and recycle the bad ones as you find them. You will make better use of your time and money that way and you will grow a team that is 100% reliable in clicking for you most days. Of course people have holidays and sickness so if they don't click for a few days, give them a chance to come back. In time, you will not have to click all 60 or so ads every day unless you want to, just a dozen or so to keep your referral clicks and make a little extra.
There are people who claim that they can live on the profits of Pay-to-Click and of course they want to tell you how, in a report they will charge a load of cash for. Don't bother with it because you'll get basically the same information I am giving you here.
I have talked about only the PTC sites where I have personal experience, I cannot speak for, or recommend others, you will have to try for yourself.
While you may not make a full time income, you could get to a position where your PTC earnings can pay for your upgrade/monthly subscription to something more profitable/useful like your autoresponder for example or your web hosting and I think that is the real secret of using PTC to your advantage.