Buying and selling on Ebay or Amazon is a pretty straightforward way of making money. You sign up with them, offer a product, and either have people bid on it auction style, or have them buy it straight up.
The first thing you will do is sign up for Ebay.
Here's the sign up link for Amazon
The next thing you will do is decide what you want to sell. You can sell websites that you've made, digital products that you can put on a cd or dvd, or you call sell what most people do...stuff from home that you can get rid of.
Another trick to buying and selling is called arbitrage. Arbitrage is offering a product for a higher price than you can get it for yourself. Say you know where to get a toaster for $9. If you know that you can sell it on Ebay for $15 then you can list it on Ebay without even owning it, have people order it, then you buy it for cheap and sell it to them.
If you want to sell a website that you've make then you might want to take a look at How to Build a Website to first learn how to make your own site. Some people would rather just buy a site already made than to make one themselves.
Just about anything and everything can be bought and sold on Ebay and Amazon. You can even put up your soul if you want to...it's been done before.
Here's a good video explaining the drop shipping process.
A good source of finding products to get cheaply and just to get new ideas of products you can sell is to use a dropshipper. Think of a dropshipper as a wholesale place to buy products cheaper than retail. What you can do is just set up a listing on Ebay or Amazon...once your product is sold you the put in an order to your dropshipper and they will handle the shipping process to whoever bought the product on Ebay. Dropshippers are a big help and keep your living room from being stuffed full of products you're selling on Ebay. Here are 2 of the most popular companies for providing dropshippers.
Worldwidebrands.com - This link will give you a $30 discount
One piece of software that some people use to build Ebay listings is called Auctiva. It just makes it faster and easier to build a nice looking listing which should help your chances of somebody buying your product.
Now, the most popular way to receive payments on Ebay is Paypal. Paypal is the most popular way to send and receive money online right now. A lot of people use it and it's really simple to use.
So here's a summary of what to do for selling something on Ebay or Amazon:
Sign up for Ebay
Sign up for Amazon
Figure out what you want to sell
Find a good dropshipper - Doba, World Wide Brands ($30 off link)
Look at the powersellers to see how to set up your listing
Receive your payment - Sign up for Paypal