Many people have recently received a letter from Coinlist, asking to create an Altair wallet address to provide to Coinlist in order to get airdrop.
You can watch this very short video to learn how to create an account with Polkadot.js.extension to get an Altair wallet address:
Once you have received your AIR in your wallet, you can watch this video to learn how to see the balance:
There is also a short written manual here where you can see the same instructions with screenshots:
Note, that there is more than one way to create a wallet address - this manual focuses on how to do it with the Polkadot.js.extension.
Also, if you have Clover wallet installed, make sure to disable it as we have seen users having issues with Polkadot.js.extension when both are installed.