To create an Extension for Loupe you need to at least create an assembly with your extension code and package it as a NuGet package. It has to have one class that implements the IExtensionDefinition Interface which describes all of the other types your extension defines.
Your assembly needs to reference Loupe.Extensibility.dll which can be found on NuGet.
Any other dependency assembly you need (except Loupe.Extensibility) should be included in your NuGet package directly. This will be automatically deployed and placed in the same directory as your extension.
Extensions are automatically deployed from the Loupe Server installation to any server in the installation and to Loupe Desktop. For complete information on deploying your Extension see Loupe Extensions - Deploying Extensions.
You can view all of the extension related runtime information from within Loupe Desktop by selecting Show Log Viewer from the backstage Support area. This will display the real-time log entries recorded by all extensions as well as Loupe Desktop as it works with each extension. For more information see Loupe Extensions - Monitoring and Troubleshooting.