Every website must have 3 things to function.

A domain name must be registered and used as an address.
     This is your .com and it is the internet equivalent of a 911 address.

Every website must be hosted somewhere.
     This is a computer on the internet that holds the website files, similar to a piece of property. The address directs web surfers to the property, or hosting location.

The website itself is a collection of files.
     This can be considered the billboard or store that is erected on the property.

So, the address points to the property where the billboard sits; the .com points to the hosting server where the website resides.