Here's a link to document.
document: Integrate a .NET Assembly Into a C# Application
For developing, rather than using installer in for_redistribution, it's useful to use .dll file in for_testing folder. In Visual Studio C# project, include this *.dll file (or *Native.dll if you want to use native .NET API) and MWArray.dll as references. MWArray.dll is located in each of the following.
$MATLAB_INSTALL\toolbox\dotnetbuilder\bin\win64\v4.0\MWArray.dll
or
$MATLAB_Runtime_INSTALL\toolbox\dotnetbuilder\bin\win64\v4.0\MWArray.dll
For C# sample code, please check "C# Code to Implement Application" of Step 5 in this document.