Respond to an e-mail from a Nigerian prince with all of your necessary details to get a million dollars.

Go get a paper round or something.

A job is going to be the easiest way to make some cash most likely.

Unless you grab yourself a fake identity and do surveys or something. I don't know if you get real money from them though since I've only done them for stuff like smite gems.

Let me be clear:
You are not going to earn any money by just doing the simple tasks like surveys (been there, done that )

But since that wasn't your question....

I earn money making "responsive" (e.g. layout that adapts to screen sizes) websites. And Bukkit plugins (but that doesn't earn much). In my opinion you always have to learn something to actually make "big" money. That's very logical look:
If it's that easy that you don't have to learn anything to do it, anyone can do it, so does the one willing to pay you. (so they won't pay because they can do it themselves).

So I suggest you learn some coding language (PHP for instance)

Get a job...its not hard im going to go ahead and assume your under 13 so 2 things
1.You don't need money
2.If you really want it go mow lawns rake leafs i did that when I was 12 and made 500$ in 3 weeks