Let's start with the question of what a domain is.
The shortest answer is that the domain is your website address.
Do you have to have your domain?
Simple answer: YES. The domain identifies the owner of the website. You should make sure that the domain is registered in your name and at your company's address.
How to choose the right domain name?
First of all, the domain name should be short and easy to remember. If you want to build a blog that will be your brand, using your name would be the right thing. You can also use your company's name in the domain, which will also be a unique name.
Where can you find and register your domain?
If you choose the hosting, I offered to you above. You will have the option to buy and register a domain. You will also get the SSL security certificate, which is indispensable nowadays.
Of course, not only SiteGround offers these services. Most hosting providers have it in their packages.
You can buy a registered domain.
Additionally, you can also search for an existing domain that is no longer used. The best place is Expired Domains, which offers domains no longer used but have a good history.
Prices are usually relatively high, but in return, you get a product with a firm position.