What charger am I supposed to use with iPhone 12 mini

Hello,

1) You can use the charging adapter and cable from a previous iPhone or

2) You can get a USB-C adapter and use the cable that came with your iPhone 12 Mini:

20W USB-C Power Adapter - iPhone Accessories 

The second option also gives you the benefits of fast charging:

Fast charge your iPhone

Good luck.

This one. It needs to have an USB-C port because the 12 mini comes with an USB-C cable.

https://www.apple.com/shop/product/MHJA3AM/A/20w-usb-c-power-adapter