It's called backlinking! See the Wiki here. Basically, backlinks are "online directories" in which websites are listed, or white pages for the internet. They are other sites linking to another site.
Many sites pay good money for backlinks, this is where you come into play!
There is a website called Fiverr where people do services for only $5. One of the things they do is create backlinks! Go with someone reputable who has lots of good reviews! They will create a certain amount (Usually 1000) for the $5.
This is where the profit is turned. Most sites pay ~$30 to get that many backlinks! You turn into the middleman!
First, you go to sites, such as WickedFire, or any other affilate marketing forums, and go to the Buy/Sell section. There you will find people looking to buy backlinks, or you can place ads for the backlinks! You can even place ads of craigslist etc.!
Once a deal is made for the price you and the buyer agree upon, you simply go to your Fiverr supplier and give the website who bought the links from you to them, and they create the backlinks for cheaper than you sold them for! This turns you a profit!
I suggest using PayPal for the monetary transactions as it is the most legitimate way!