Name Spaces in C# and how to access external libraries

BACKGROUND

I have a free trial of unity pro, and am using QCAR augmented Reality. I am new to C#, (but well versed in JS), so I would appreciate some help using namespaces.

I want to use the method called projectPoint, described in the QCAR documentation here: https://ar.qualcomm.at/qdevnet/api . projectPoint usage is below:

QCAR_API Vec2F QCAR::Tool::projectPoint ( const CameraCalibration & calib, const Matrix34F & pose, const Vec3F & point )

QUESTION

How can I call this function inside C# script? And, what are the necessary imports/include(s)/namespace requirements?

PAST ATTEMPTS

Note, QCAR has been properly installed because the demo code from Qualcomm works fine. However, they don't use projectPoint or any similar function so I couldn't learn the usage from the samples.

I have tried and get the following errors:

1. include QCAR (Error: QCAR is a type, not a namespace)

2. using QCAR::Tool (Alias QCAR not found)

just executing the function in my C# class, I also get errors:

1. QCAR.VideoMode videoMode = QCAR::CameraDevice.getInstance().getVideoMode(CameraDevice.MODE_DEFAULT); (The nested type VideoMode' does not exist in the type QCAR')

2. QCAR::VideoBackgroundConfig config = QCAR::Renderer::getInstance().getVideoBackgroundConfig(); (error CS1525: Unexpected symbol `::')