How do I do a site like this?

I have an idea for a CPA incentivized site where users complete surveys and after they earn a determined amount of points, win a steam game for free.

I know nothing of web design. How can I do a site like this?

Its called a GPT site. There are thousands of them.

Either google GPT script, or buy a custom built one. If you are serious about it though, i would go with the custom script. It will make youbstand out from the thousands of others