How I connect mini display port VGA to iPad?

Presumably you enquiry relates to the Apple Mini Display Port Adapters - described here:

About the Apple Mini DisplayPort adapters - Apple

These Adapters are not compatible with iPad.

There are, however, VGA Adapters that are compatible with iPad. Depending upon your iPad model, it will have either an Apple Lightning or USB-C port. You’ll need the VGA Adapter that matches the port on the iPad:

• Lightning to VGA Adapter

https://store.apple.com/uk/xc/product/MD825ZM/A

• USB-C VGA Multiport Adapter

https://store.apple.com/uk/xc/product/MJ1L2ZM/A

When using USB-C cables, you would be best advised to use a cable with the correct connectors. The USB-C standards do not promote or support use of simple plug adapters - as these lack the protective active circuitry that is built-in to certified USB-C cables.

USB-C and Lightning also differ in that they use different electrical and signalling standards - for which an active interface converter is required; the interface converter is incorporated within the plug of the appropriate cable.