Website adresses such as youtube.com and google.com is called domain name. Registering a domain name costs approximately 10 USD $ for a year. If you want to register a domain name, you have to pay between 5 to 15 bucks. You, otherwise, have to use free subdomain name such as yoursite.hostingcompany.com. I suggest you to register a domain name because if you need to move your website to another hosting package, your website adress remains the same.
Some web hosting companies gives free domain name if you buy a paid hosting package. If you wont buy one of those packages, you can register your domain name from godaddy.com, the biggest domain name registrar in the world.
If you register a domain name, you should make the connection between domain name and hosting package. After registering a domain name, you should change domain name's nameserver settings and point it to your hosting package. Later, you should add domain name to your hosting package from control panel of your hosting package. If you do not know nameserver adress of your hosting package, you can learn it from the control panel of your hosting package or from web hosting service provider.