Hosting might seem complicated but it's not really. When you look at things online - a web site, an image or a pdf - they have to be stored somewhere public so that everyone can see them. If you just have an image on your computer no one can see it but you, and you'll end up with a blank spot in your email.
Hosting is a service provided by web hosting companies which offer a physical location online for web pages and files. It's helpful to think of it as a type of landlord, they rent physical space on their servers allowing web pages and files to be viewed on the Internet.
Some VerticalResponse customers use Dropbox to host images or files that they want to include in their emails as links. Check out how to use Dropbox here. For images you can also take a look at flickr or Photobucket, or do a search and find one that you like. If you upload an image to your VR account we'll automatically host the image for you, so that your readers will see it in your email.
VerticalResponse hosts the web version of your email, which allows you to link to your email on social media and allows email recipients to view your email in their browser from the hosted version link.