How to use the @babylonjs/core/Cameras/freeCamera.FreeCamera function in @babylonjs/core

self._engine = new Engine(canvas, opts.antiAlias, {
        preserveDrawingBuffer: opts.preserveDrawingBuffer,
    })
    self._scene = new Scene(self._engine)
    var scene = self._scene
    // remove built-in listeners
    scene.detachControl()

    // octree setup
    self._octree = new Octree($ => {})
    self._octree.blocks = []
    scene._selectionOctree = self._octree

    // camera, and empty mesh to hold it, and one to accumulate rotations
    self._cameraHolder = new Mesh('camHolder', scene)
    self._camera = new FreeCamera('camera', new Vector3(0, 0, 0), scene)
    self._camera.parent = self._cameraHolder
    self._camera.minZ = .01
    self._cameraHolder.visibility = false

    // plane obscuring the camera - for overlaying an effect on the whole view
    self._camScreen = Mesh.CreatePlane('camScreen', 10, scene)
    self.addMeshToScene(self._camScreen)
    self._camScreen.position.z = .1
    self._camScreen.parent = self._camera
    self._camScreenMat = self.makeStandardMaterial('camscreenmat')
    self._camScreen.material = self._camScreenMat
    self._camScreen.setEnabled(false)
    self._camLocBlock = 0

    // apply some defaults
    var lightVec = new Vector3(0.1, 1, 0.3)