Use the Check for Updates facility of the Platform (in the Windows Start menu under ASCOM Platform) to make sure you have the latest versions of the developer components. Also see the Additional Tools page for more developer tools (such as the Conformance Checker) not included in the Platform Developer Components.
This installs the ASCOM Platform Developer Components on your system.
The Platform development team has done quite a bit of work to assist driver developers who use .NET languages. .NET is Microsoft's supported development environment, with C# being the recommended choice of language, and Visual Studio 2022 as the Integrated Development Environment. For those who are starting driver development, it is suggested that you use VS2022 and C#, and use the appropriate driver project template we have provided.
During installation of the ASCOM Platform Developer Components, you'll see info on installing the templates which are an Extension in Visual Studio:
Once you have the templates installed, when you create a new Project in VS and it asks you for a template, choose the ASCOM template type, then follow the prompts. Along the way you'll see a nice detailed help document appropriate to the device3 type with a guide on how to go forward from there.