How does "godaddy.com" create domains and why can't you do it yourself?

[Beamin]

I have always wondered how this company does this. Why can't you register one yourself or who is the governing body that makes this if its all decentralized, long before block chain was invented?

Whats also strange is you can buy a "new" domain for a few dollars then turn around and sell it for a huge mark up. (Anybody want to buy blackfridayboycott.com and .org? I have been sitting on those and 40+ others for sometime) but I don't understand why go daddy would not mark up more desirable names like computers.com right off the bat.

What keeps someone from just hijacking your domain or outright stealing. Imagine if you stole google.com for a day and put up a some ads? When I was a kid I knew the internet would be big and tried to get my father to register some but he wouldn't do it. I could be retired if he did because I wanted to obtain the names of all popular brands. Think of typing "cocacola.com" and getting an error 404 or "this domain is for sale for 12.99$ per year"?! 

[Ampera]

Long story short: https://en.wikipedia.org/wiki/ICANN and https://en.wikipedia.org/wiki/Internet_Assigned_Numbers_Authority

Long story not as short:

ICANN (at least at the moment) is the organization responsible for assigning what's called TLDs to registrars, using their subsidiary IANA, formerly owned by the US government (the internet is a US government thing).

Put very simply they are the people who give out the privileges to manage domain names to various companies or organizations, and also will take a small annual fee whenever you register a domain name.
Authorities that get given the ability to manage TLDs, for example VeriSign who manages .com, .net, and a few others, may or may not do the business end of registering a domain name themselves. If one were to go onto VeriSign's website and look around, you'd quickly notice that they don't sell you domain names, and instead lead you to a company that will.

These companies, like godaddy, are effectively brokers for domain names. They handle the somewhat complicated task of figuring out who needs to get paid (while also taking a cut) for the many many different domain name authorities out there, as well as providing secure access to modify the DNS records for that second level domain on the DNS root servers, which get propagated along the chain.

Not all domain name authorities are like VeriSign though, and there are many, particularly with ccTLDs (country code TLDs like .de .uk .su .us .yu .sm etc) that will handle the registration themselves as the domain authority. These authorities will often want specific restrictions put in place, usually citizenship, mailing addresses, or business interest in their nations. They will also often still allow brokers like godaddy to register domains with them on your behalf too, which is why you can still find those TLDs on their websites.

As for why a random person can't just go redirect google.com to their own page and throw some ads up, in general the requests to modify entries on the DNS root servers (I believe, all of this is research mixed with a bit of speculation, so I could be wrong) go through the IANA, and they ensure that only specific authorities have secure access to modify records for their TLDs, and those authorities secure their own registars.