There are tons of ways you can earn money online.

For starters, you can answer questions here at WebAnswers or at other Q&A websites such as Student of Fortune, Just Answer, Cha Cha, Answer Gem, Mahalo, Help Owl, Weegy, etc, etc.

You could also make money by writing articles on websites such as Hub Pages, Squidoo, Triond, Fire How, Bukisa, etc, etc.
You might try doing freelance work on websites like Freelancer, eLance, or Odesk if you have some profitable skills that could be put to use there.

Then there are also some survey sites where you can make some spending money, like QuickRewards (.net), Mind Field Online, ePoll Surveys, Esearch, Opinion Outpost, Global Opinion Panels, Survey Savvy, Global Test Market, etc, etc.

And finally, you could try selling items on eBay. You might start by selling things you have around the house that you don't need.
And then you could go to yard sales, flea markets, auctions, discount stores, etc, and buy your goods that you think you could re-sell for a higher price on eBay.

There are probably many other ways to earn online but these are some popular ways that people do have success with - answering questions on sites similar to this one, writing articles, doing freelance work, taking surveys, and selling on eBay.
Hope this helps and best of luck!