When I connect to macbook, I can’t extend the display of my desktop, why?

If you select non-mirror(extended mode) for OS systems laptop (Apple Laptop), it can only supports 2 duplicate (mirror) external monitors, but your laptop screen can not be different image from 2 external monitors due to apple system restrictions.

Why is my laptop screen black when I extend 3 monitors on my windows system laptop?

For Intel Graphics Card, it only supports 3 screens display, thus one of four screens (including laptop screen) will not be displayed. For AMD Graphics Card, all of four screens will be displayed.

When I plug in VGA port, why does the resolution become 1920 x 1080@60Hz?

Please do not worry. This usb c hub supports 4K@30Hz HDMI OUTPUT (depends on your HDMI cable and monitors). If you connect VGA, the resolution of all monitors will be limited to 1920 x 1080@60Hz (maximum).

Why does one of monitor resolution become lower than 1920 x 1080@60Hz, when I extend 3 monitors from my windows laptop?

In normal, when you connect 3 monitors, all of three monitor will output 1080P resolution. However, it may happen that one of the monitor screen resolution is lower than 1920 x 1080@60Hz (depending on the monitor and bandwidth).

Why do I have no display when the dock station is connected?

a. Make sure the type c power delivery port on you laptop is USB 3.1 Type-C (Gen2) or Thunderbolt 3 port (supports PD charging). That means the native type c port of laptop need to support video signal output.

b. Check your HDMI cable.

c. Ensure sufficient power supply from the USB C hub.

When I plug in or plug out on this docking station, hdmi or VGA monitors go black for 2–4 seconds and then recover? Is this normal?

Please do not worry and be patient waiting for it. It is a process of EDID (Extended Display Identification Data) communication, which may blackout screen for a few seconds. The recovery time depends on laptop and monitor (1 minute at max).