What Things Can I Put on a Blog?
Basically, you can put anything you like on a blog. I'll run through the most common things, so you know for sure.
Video & audio
Blogging systems almost always allow you to post videos, but require that you host those videos elsewhere (like YouTube or Vimeo). This is typically very easy to do. Some will allow you to host audio on their own servers. In WordPress, you can just paste the address of a YouTube video into your blog, and visitors to your blog will see the video there.
Although it's not usual to sell on blog, you can easily sell your products (or other people's products as an affiliate) on a blog. To sell a few products and accept credit card payments, you can easily add PayPal "buy now" links to your site. For anything more complicated, you'll need a specific eCommerce system.
Social networking / facebook connection
It varies from system to system, but almost every system allows integration with Facebook and other social networks.
Yes, you can upload any kind of other files, like Word, Excel, or PDF files to your blog. What you can't do, however, is copy the formatting from one of those files to your blogging system. You either need to paste in the text and images from your file, or just upload the whole file, and have it available for download.