There are many ways that you can earn from your site, all of which take a good deal of work.
To be clear, there are many who believe that simply having a website is more th 90% of the battle. They are wrong. Having a website is the easy part. Getting people to your website consistently is 99.999999% of the battle. Websites in this day and age can come by any number of ways, whether it be paid for as a custom built website, or whether it be by way of Spruz or numerous other similar resources. Anyone can build a website in less than an hour. The big "Question" after knowing all of this is.. "Who really cares about what you've done?".
While all above may sound somewhat brutal, it's supposed to. No one cares, mainly because no one knows. That's the name of the game. How do you get people to know what you have done, and then once they do, will they really even care? So let's expound upon that thought for a minute. What would people care about? Would they care that you've successfully created a social network about... something that 100s of other people have already done, and much likely better? Probably not. Would they care that you are the "next facebook"... Definitely not. So what is it that people would care about exactly?
Do you have content on your site that is hard to come by? If you answered yes, then you are on your way to creating a site that people will want to come to. It doesn't matter how you do it, it only matters that you do. As it turns out, this is the largest issue in a successful site, as well as monitized site. Whether you want to sell ads on your site on a per viewer basis, or rather you simply have a product to sell, you have to expect that your site has to fulfill a need that has not already been met. It's basic product and supply business concept.
So in the case of advertisements alone on your site making money, you will need to provide content that really delivers in a way that no one else can. It will need to be 1 - unique, or 2 - delivered in a unique way. This could gain you an audience that would generate revenue in regards to ads when clicked on.
In the event you are selling products, you need to aski yourself if you are the "only person(or really close) who is selling the product", or are there already hundreds of people offering the product who already have more money than you do, who can afford 10 time the advertisement campaign to bring people to their website. If there are others who are already highly successful, it's a problem.
To earn money from your site, you have to offer what others can not, and it's a wide open statement, but just as accurate as it can be.