What is the difference between UNIX hosting and Windows hosting?

The operating system to go with depends on your needs.

If you need to support Microsoft products such as ASP, MS Access, or VBScript, then Windows hosting would suit your needs

All other technologies will be better placed on a linux hosting plan.

There are some things to remember:

Just because you use Windows at home does not mean you should use Windows hosting. The two are completely different, and having a Windows system at home will not affect your ability to communicate with a UNIX / Linux server or to host your php,html,htm, frontpage, publisher websites!

Linux is much more common with web hosts due to its superior stability and due to many distributions being open source. The majority of the web is server from Linux machine / servers.