This Module has another name: Gert-VGA-adapter, or Passive VGA adapter 666 for Raspberry Pi A+/B+/2B/3B/Zero
The Raspberry Pi has an HDMI port to connect a display.
If your monitor only has VGA, you have to use an adapter. 
Because this requires a digital-to-analogue conversion, those adapters can be quite pricey, and they can draw lots of power.
As well as just allowing you to connect a VGA monitor natively. 
And unlike composite video, the DPI interface can be run independent of the HDMI. 
The software for dual screens is still under development. 
Running two screens at maximum resolution will depend on the speed of GPIO.
This wasn’t possible on the Model A or B.
And there’s a catch: as the board uses most of your GPIO pins, you lose access to them.

All above are from raspberry pi official website.
More information about VGA666 module please visit here.

Features

• Support for Raspberry Pi A+, Raspberry Pi B+, Raspberry Pi      Zero, Raspberry Pi 2,model B, Raspberry Pi 3 model B

• The VGA output supports resolution:from 800x600 up to 30fps.

• With 6 bits per channel you have a maximum of 262144 colours.

• Easy to setup.

• Easy to configure.

• Dimension: 64.00mm x 32.24mm

• Weight: 16.48 g

Part List

1 x VGA666 module