Buying domain is an easy job, but I think you should select the one which suits your business and goes with its name. Also, if you want to find the name that has not registered before use the reputed domain name registrar like Domain.com, Hover and MilesWeb.
If you want to purchase a domain name that has already been registered you can do that also. But it will be a complicated process plus you will have to pay a huge amount for it. So, I will advise you to buy the new unregistered domain name.