Answer:
It's actually very easy. The hardest thing is finding the legitimate survey sites in the pile of frauds. The frauds are usally pretty easy to pick out once you get the hang of it. If something says you can earn $500 a week without doing anything, or by doing surveys it's definitely a scam.
You will only earn $5-$100 per month doing online sureys, and that's only if you do them whenever you get them. Some surveys are very long and boring, so brace yourself.