Simplifying Complexity, One Answer at a Time!
Rules
So called root servers are registered with the IANA. They are basically the seeds for the federation. There are rules what these root servers need to do and how they can be queried - and from those few servers it gets spread around the world - but not federated as in "everyone can write back", there are rules who can add what when.
They also tell who owns top level domains (.com, .net, .de, etc). The other replier is wrong: they do not sell individual domains.
DNS is more a tree then a flat network, the root DNS servers host all the top level domains. Think .com and .UK and all the country codes.
Below that are DNS servers that host sub domains, below that are caching DNS servers that an ISP might run or your own DNS.
What is added to root DNS servers is in the hands of IANA, they allow new top level domains and where sub domains live.
The sub domain DNS servers are managed by the owners of that sub domain, so I own horwood.biz and can decide where that domain is hosted and what the hosts in the domain resolve to.
When you look up my domain, you might find that a query to a root DNS server is done to find the owner of .biz and then from that a query to find my DNS server and finally a query of the DNS server for horwood.biz.
but how are there multiple DNS server
DNS servers are just phone books. If you want to connect to maps.google.com, you can do it in two ways:
You can ask .com who hosts google.com, then ask google.com who hosts maps.google.com (this is called recursive lookup), it's a slow process relatively speaking, especially when you may need to do it dozens of times to open a single webpage.
Alternatively, you can go to a "phonebook" like Cloudflare's 1.1.1.1 or Google's 8.8.8.8 or any one of a million others and just ask them for the info. They're constantly getting these requests so they save the info in their cache and can just pull the direct IP. If they don't have something cached (rare, except for very new or u popular domains), they revert to step 1.
how can there be DNS outages when there are multiple DNS server
Because most devices are set up to query up to 2 DNS servers, one primary, one fallback. If both fail, (or if only one was configured from the start) that device will have issues. If that device is a critical link in the world wide web, the failures cascade. If your non-tech-savy grandmother is running on the default DNS of her ISP, and they're pointing their servers at Cloudflare because its faster, then if Cloudflare's DNS goes down, her internet seems to go down.
Also, even if you have a backup solution, Cloudflare DNS handles likely trillions of DNS queries each day. Easy enough for them, but when they fail, all of those queries suddenly hit other DNS servers like a DDOS attack, which can cause failures and propagation down the line.
And does every government have there own DNS servers that point to the main ones?
Generally, probably no. Some government agencies may be paranoid enough to run their own DNS servers that do recursive lookups etc, but I'd wager many just use whatever's default in the OS. CIA certainly rolls their own, but the City Council of Des Moines, Iowa probably doesn't. A bad DNS server could run some pretty sophisticated MITM/phishing schemes, so there very much is a risk there though.
so there are two aspects. as people have said it goes sorta reverse of the name. so there is the root operated by ican that directs to the top level domains like .org which directs to specific addresses like eff. Thing is there is stuff that is publically made available and internal ones and this has to do with where a person gets their directory. So people who work for eff likely have a dns provider in the list their machine uses (they can have one or many listed and it checks it in the order its configured in) that is from the eff. this allows them to find all the machines from eff. But if you are looking for machines there you will have a provider getting public machines from eff and that will only be a list of machines the eff wants to be publically available. As an individual you will use a dns that either you configured or was configured by some process you did. Like your isp will generally have one available and if you don't specify what to use in your config it will grab the information along with other network information from dhcp. The same process that you get your ip address with. You could go in though and change that (just realized I never did when I reinstalled my machine) and in addition software you run can override that. Like you can set dns servers to use in your web browser.
All domain names are allocated by IANA. They sell IP addresses and domains in bulk to resellers, you buy it from them.