A domain name shouldn't exceed 2-3 words and shorter names are easier to remember and type. Don't use complicated or uncommon words that may be hard to spell or remember. Use relevant words that allow users to find you in a search and recognize you at a glance. Your domain name should reflect/be similar to your brand name and don't use existing brand names or trademarks. Don't include numbers, dashes, funny spellings or words, misspellings, or other brand names and trademarks in your domain name.
A domain name can be bought from a domain registrar. First, you use a domain availability checker tool to see if your domain name is already being used. If not, you can then pay for it for one year at a time or pay for multiple years at once. Prices depend on the Top-Level Domain of your domain name.
I am running a bakery shop called Mr. Z's Bakery. It is a world renown company with many locations. My domain name is mrzbakery.com. It is a good domain name because it is a simple and short domain name. It references the type of business it is and includes my name so everyone knows it belongs to me. It is also very similar to the company's name. It is spelt right and doesn't use other names or trademarks already in use. It is also available.
Domain Availability Checker