At this stage everything becomes a little more complex and the financial factor interferes. If you want to register second-level domain name (one word before TLD or root zone, for example, BOBA.net), you'll likely have to pay for it. Though you may be able to get a free domain name from one of web hostings for certain kinds of activities. With the third level domain names things are going better and now you can get it for free from almost every web hosting, but it will be neither so neat nor so memorable ...
By the way, registration of second level domain names often involves serious problems, even if the name of a registrar is quite popular. If anyone interested, look for materials on the scandal associated with ENOM and REGISTERFLY. So your money will not always guarantee a quiet life for you. To avoid such a situation it will be wise when registering for example fifty or more domain names to use services of several different companies. Or choose a company that you can "physically" reach.
For reference. Every computer connected to the Internet has a unique IP-address, consisting of four numbers, each of which may have a value from 0 to 255, separated by dots (e.g., 255.255.255.255). To convert the IP-address in a form more acceptable for a human being (let's say, to the same BOBA.net), there exists a hierarchical naming system - DNS. The domain name level is defined from right to left: the first position before dot occupy TLDs, originally they were based on organizational ( com, edu, etc.) and geographical (ru) principles, the second-level domain looks like our desired BoBa.net and at last third-level domain - BoBa.combination_of_several_alphanumeric_characters.net. Prefix - http://www - defines the service used by the Internet - www and data transfer protocol - http.