This guide will show you how to install datapacks to your server.
Disclaimer: datapacks are worse performance-wise than plugins, use plugins where you can!
Step 1: Download your desired datapack. In this example, I will use the "CavesAndCliffsPreview" datapack from Mojang. https://launcher.mojang.com/v1/objects/622bf0fd298e1e164ecd05d866045ed5941283cf/CavesAndCliffsPreview.zip
Step 2: Go to the Raw Power Panel and select the server you want to add the datapack to.
Step 3: If the datapack you downloaded is in .zip, you can skip this step. If the datapack you downloaded is a folder, use 7-Zip to make a .zip or .tar.gz archive. Please keep in mind, that .rar and .7z is not supported, only .zip and .tar.gz is.
Step 4: Stop your server, navigate to file management, open up your world folder, and open the heading "Datapacks".
Step 4: Upload the datapack to your world directory. You can do this using either the Upload feature from File Management, however using SFTP client like WinSCP is recommended. If you don't know how to connect using a SFTP client, have a look at this guide.
Step 6: Start your server, and monitor the startup. It should display the name of the datapack, which indicates that it has loaded correctly.
And there you go! You have now installed a datapack on your server. Remember, read the documentation carefully of each datapack, as some of them can modify your world, and will not allow you to boot your server if you try booting it without the datapack installed.