This is something any small business owner needs to know. If you do not know, this lack of knowledge can sneak up an bite you at the worst possible time. Imagine if your website disappears from the Internet during the busy Summer season, yikes! If your domain name does not get renewed, and becomes available to the market, you will have a mess of epic proportions to deal with.
There are many domain registrars. And spammers rely on this fact. They will send you fake invoices, and if you are not paying attention, they will charge you 4 or 10 times the going rate for your domain name. And worse, they move your domain from wherever it was to a new and different, possibly less reliable registrar. Technically legal (maybe, I am not a lawyer), but morally reprehensible. And… it makes it even harder to know where your domain is actually registered. SO PAY ATTENTION TO YOUR DOMAIN REGISTRAR!
The big ones are GoDaddy and NameCheap. There are many others too numerous to name here. I personally recommend a company called Hover. Domain registrars are famous for upselling, which gets very tiresome. Hover does not do this. A breath of fresh air.