There are many ways to create a library project. Please explain what you have created and your solution or zip it and attach it to a reply here or email to info[at]visualmicro.com along with link to this thread.

Which board have you got?

Currently the arduino.h header from the arduino core can not be found in your library because you have not added a normal arduino project that uses the library.

The readme in the new library project that you have created gives you some ideas. It says the library works like a normal arduino library. An Arduino library is not a self contained executable project and it not tied to any specific hardware.

You need to add an arduino project to your solution so that you have both a standard arduino project and the library project. Then follow the readme which explains how to add a reference between the arduino project and the library project so that a) intellisense can work and b) your arduino project can find the library outside of the official arduino library locations

You can negate b) is you ensure the library is created below an official arduino libraries location such as mydocument\arduino\libraries. In this way the arduino ide will also then be able to see your library. However you can right click > publish  on the library.properties file to have the library automatically copied to the official location at a time of your choosing.

Visual Studio has the concept of a "Startup Project". The Startup project name is shown in the solution explorer in bold. A library project will use the board/hardware selection of the Startup project if the reference mentioned earlier has been added.

This enables you to have a solution with one or more library projects referenced from one or more Arduino projects. Each Arduino project might have a different board assigned. When developing the library the intellisense will be for the board of the Startup project.

note: I have changed the subject of this thread. I suggest that you do not refer to .h files as libraries when discussing arduino