Hi Catherine,
You can sign up via the Amazon website. Look for the links to Amazon Associates and how to become one. It's very self explanatory as far as signing up. Then, look for the widgets and banners tab, add product link, etc. You simply have to find the product, click to get a product link/buy button, copy and paste into your article when you input.
As for links into forum posts, you must use UBB code. You can find a very good tutorial in the editors courses section of your admin page.
It is easier than I made it sound, I promise.

You can ask your BOL mentor or training manager, too. They really know this stuff.
I'll wait to buy until I see your link on your page!