D&D Beyond encourages all of our community members to build and create custom content on our network in a positive way. While each section of the website might have their own local guidelines and policies, all community members are subject to the Wizards Terms of Use, found here: Wizards Terms of Use.
The specific rules and guidelines for homebrew content can be found here: Homebrew Content Rules & Guidelines.
You will want to familiarize yourself with all of these rules and guidelines before creating your own content.