One of the biggest reasons people want to get online is to make money. This is very understandable. The problem is that it can be expensive. To collect money on a site, you need to provide a safe way to input financial information. This usually involves paying about $300 per year for a security certificate and configuring your web server to make secure connections with visitors to your site. Add to that the cost of credit card processing, which you pretty much have to outsource to another company. This can be worthwhile if you have a lot of sales every month. As an example, one credit card processor will sign you up for free (advanced features can cost you up to $349 in setup fees) and charge you $48 per month and 50¢ + 2.99% per sale.
If you're starting out (or you like saving money), I recommend PayPal®.
PayPal is owned by eBay®. As a PayPal merchant, you can sell as many products as you want and it is fairly easy to setup. They have wizards that walk you through the process of changing your web page to use their service. You don't have to do anything to your web server. Visitors to your site can pay through PayPal whether they have PayPal accounts or not. For businesses, you can sell items on your site for a fee of 2.9% + 30¢ on each sale. So if you sell a $10 item, PayPal will take out 59¢. It's fairly reasonable for no monthly fees, setup fees, or web server hassles.