Please check Custom Domain FAQ before reading further.
Please note this tutorial is for Bluehost (affiliate link to support organization).
Please note you should follow this only when you are absolutely sure you want to use the top-level domain.
For example, if your domain is domain.com, and you have a blog, portfolio or some important content there, and follow this, it will erase everything. If your domain.com site is already occupied, either purchase a new domain or use the subdomain solution i.e. solution 2.
Solution 1: Using top level domain e.g. domain.com
Solution 2: Using subdomains, e.g. webinar.domain.com