Domestically, VAT rules have not changed after Brexit. However, if your company trades to and from the EU, you need to take note of the new VAT rules.
As of 1 January 2021, UK businesses have to register for VAT in each EU country. There are no more common rules with the EU pertaining to VAT. UK businesses will not be able to use VAT simplifications such as distance selling thresholds or the online VAT refund process.
When you trade with the EU, it is referred to as imports and exports too.