There are many way to earn money. One of fastest growing trend is blogging for money. You can create a free blog at www.blogger.com
If you already own a blog here is some tips to generate some extra cash.
Affiliate programs: If you really want to make some extra money with your blog you can add affiliate links to your blog, when someone buys through your personal affiliate link you get commision.
Generating traffic: If you have a plenty of affiliate links on your blog no one is visiting your site, you never will make any profit. To get free traffic you got to submit your blog to free blog directories. You can find free blog directories with entering free directories to your search engine. Make sure you update your blog once a day.
Make sure you blog about something, within your interest.