Go to the domain name registrar you chose.
Type in your domain into the search box and click Search Domain.
Select the extension you need (for example .com or .biz) and add the domain to your cart.
Complete the registration process and make the payment.
Domain registrars might prompt you to buy additional features, so before paying make sure there are no additional items in your cart that you don't need.
The domain is now yours.
We strongly recommend purchasing an SSL certificate for your domain. See our guide about HTTPS and SSL for details.