How to access my website without entering the FQDN, just the domain

To access my website (just a testing page for now) I have to enter hostname.domainname.com. I would like instead of just entering the domain name (domain.com).

Do i have to configure BIND, do I need an other application or do I need to change the Domain Register (CloudFlare).

Currently on Ubuntu Server 18.04 Fully update!

Sorry for my bad english! And thank you!