All online jobs are a scam and any sites asking you to pay to join to make money are scams. However it is possible to make money online without spending any money. It won't make you rich and it is not a job, but generally the more you do online and the more time you spend online the more you can make.
The main way many people make money online is through their own website or webpages. Of course, if you've no clue how to make a website that is not the best option, but there are still other options based on that. The first is to sell online. Ebay is one option. The other is to use a site where you can get paid for writing content such as articles or reviews. One great site for this is Squidoo which is really easy to use. Check out my links below for help on ebay and Squidoo.
Help on ebay: http://www.squidoo.com/ebay-site
Getting started on Squidoo: http://www.squidoo.com/writing-a-lens
The next option is to write reviews online. For this Ciao and Dooyoo are very useful sites. You can write one review, place it on both sites and get paid for it. You can write reviews on pretty much anything you can think of; DVDs, games, music, clothes, websites, shops and more.
For more info: http://www.squidoo.com/ciaosite
Another good way to make a bit of extra cash is through surveys. The surveys are free to do and range from watching a short video clip, to registering on a site, to completing a survey on a certain topic. There are plenty of easy surveys to do that don't require giving out a lot of personal details (if that's something that worries you).
For more info: http://www.squidoo.com/points2shop-cashle-site
My proof that it works: http://www.squidoo.com/points2shop-proof-page
As well as surveys there is also another site that gives you cash (or items) simply for using their google powered search engine. You can also play games, watch videos and complete the dailies (e.g. answering a poll) and get paid for it.
For more info: http://www.squidoo.com/swagbucks-site
All these sites are 100?ree to join and use! Some even give you a bonus just for joining. How they work is by advertisers paying them for advertising their product/services and the sites all give a percentage of that money to you.
There are of course many other websites; some good and some scams. So to make sure you don't get scammed check out the this site, http://www.squidoo.com/avoid-the-scams.