The front end is what your visitors will see when they come to your website. Many of the tasks performed on the back-end will be visible on the front end, such as theme customizations, plugin functionality enhancements, and content publication. Actions can also be performed by you and your visitors directly from the front-end of the website, including commenting and social sharing.
Hi A S, Picking and purchasing a domain name and start building your website go hand in hand. What usually happens is that you test out a few different website builders to see which one you enjoy working with and has the tools that you are looking for. During that time, you can also start your search for your domain name. This is usually your business' name or brand name. We have a domain name guide here. Once you settle with a website builder and decide to upgrade to a paid plan, you can then connect your domain name to the website. Each website builder will have tutorials on how to do that. Hope this helps! Jeremy