system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do sites like GoDaddy have access to domains to sell?

Also, are there any regulations?
gpt
ICANN (Internet Corporation for Assigned Names and Numbers.) is in charge of .com domains (as well as many others.  They are a non profit, and certify any reseller such as GoDaddy.  

They also charge an annual fee for any domain name you register, which funds their operations.   

So GoDaddy gets certified by ICANN, and is now allowed to register any unused ICANN name.  For each name they register, they pay ICANN.