One of the simplest forms of making extra money on the internet is through sites known as GPT (Get Paid To) sites. The most famous one of them all being SwagBucks.
Some people confuse these for paid survey sites, but they are not!
These are basically a form of online rewards program where you are rewarded for doing a variety of online tasks, from reading emails and completing offers, to shopping online, visiting advertiser websites, and so on.
They may have a survey for you to take here and there, but they are not actual market research companies that conduct studies.