The wifi sharing feature allows you to share 3G connection with others via Wifi signal.
Here's how to share 3G as Wifi on Xiaomi Mi A1:
Step 1: Go to 'Settings' and select 'More'.

Select 'Add'.
Step 2: Select 'USB internet & mobile hotspot'.

Select 'USB internet & mobile hotspot'.
Step 3: Turn on 'Mobile hotspot'.

Turn on 'Mobile hotspot'.
Step 4: Set up password and wifi name.

Set up password and wifi name.
That's it, you have completed the setup. Wishing you success.