I downloaded Holographic Displays earlier today, When i attempt to use it i get 'org.bukkit.command.CommandException: Cannot execute command 'hd' in plugin HolographicDisplays v2.3.2 - plugin is disabled." in console. In game, it says Internal Error.
How do I enable the plugin?

Check the logs next time. As for now plugin only works up until 1.13.1

Dev Builds do work on 1.14.3 @YouHaveTrouble
Don't spread semi-true information

First of all, try the latest dev build. I'll reopen the issue if you provide logs with the latest version. Make sure you're using Spigot and not just CraftBukkit.