Check out example codes for "c# postmessage mouse click". It will help you in understanding the concepts better.
Code Example 1
[DllImport("user32.dll")]
static extern bool PostMessage(IntPtr hWnd, uint Msg, int wParam, int lParam);
const int WM_LBUTTONDOWN = 0x0201;
const int WM_LBUTTONUP = 0x0202;
PostMessage(hWnd, WM_LBUTTONDOWN, 1, 0);
PostMessage(hWnd, WM_LBUTTONUP, 0, 0);
Learn ReactJs, React Native from akashmittal.com