Visit https://metamask.io/download, then install. You can also download on the mobile app stores. Be sure to keep your seed phrase in a secure location and never give this out to anyone.
Hit the Buy BNB button. You can pay with your credit/debit card, Apple pay or Google pay.Send it to your Metamask wallet. Swap for MMA.
Ensure your wallet address is a Binance Smart Chain address which starts with "Ox".