The IP addresses used by computers on Internet to communicate are, most of the time, not static. Except if you own a professional access, your IP isn't static and is changed regularly by your Internet Service Provider. If you want to host your site on your computer, you need to install a program that will make your IP matches a domain name, and dynamically change it, thus making your site always accessible, independently of your current IP.
Some sites can provide you this service, and most of time they also offer you e-mail services. The two most famous are :
