How exactly? Let me tell you about my current favorite site, Cashnhits (refer to "Favorite Legit Site" tab for more info). I'll show you the difference in earnings with referrals. I'm not going to BS you with outrageous earnings. These are my up to date earnings as of today.
I currently have 50+ active referrals on this legit ptc site. I purchased some of them as permanent referrals from the site and I have gotten my money back already. If you want to know my exact methods I used, refer to the tab "Discover Referral Tips."
This is my personal and real example. Please consider that I am an upgraded member.
Here is how much I would earn without a ptc referral
PTC ads - 6 cents
Video ads - 5 cents
Autosurf - 22 cents
Total Daily earnings without ptc referrals = 33 cents (Very good for a ptc site)
Here is how much I earn with all of my ptc referrals (higher referral commission due to upgrade)
Average Daily referral earnings - 80 cents
Total Daily earnings with ptc referrals = $1.13
Note: Upgrading will make your referral experience much better. It is much more wise to obtain a considerable amount of referrals first before purchasing the upgrade.