Computers don't understand human language. They only understand "mathemathic language". Language used for communication between servers on the Internet, is constructed in the same way. When you are visiting a web site, for example onet.pl, in reality your browser (your computer) is connecting with other computer, which real network name is for example: 213.180.141.140. This digit sequence is called IP number or IP address.
Of course, if we had to remember those digit sequences (or even more difficult version: 2001:0db8:0000:0000:0000:0000:1428:57ab), life of Internet users would be much more complicated. That's why domains were created. Domains are names of WWW servers written in "human language", which are translated on IP numbers (user don't have to worry about it).
If assinging of server names would remain without any control, then we would have a big mess on the Internet. To avoid that kind of problem special institutions were created, which are responsible for assigning of free names to specific customers, who can later assign them to specific servers. So, if you want to get your own name (domain, for example servizza.com), you should contact an institution (most often to one of authorized partners like Servizza) responsible for handling of given domain type (example.com, example.pl, etc.), pay for it, and then assing it to your server.
Of course, it doesn't mean that every web site has to have its own address, it can containt for example, a subdomain, which is an added address to another address, or custom catalogue of other domain. He is an example: 'your_site.other_domain.com' or 'other_domain.com/your_site, instead of: 'your_site.com'. It all depends on preferences and needs, size of service, its character, etc. However, in most cases we would like to have our own, unique address, so - let's do it!.
