Instructions are similar for Mac, Android phone and iPhone. Only difference is download source.
Go to https://blockstream.com/green/ and select the appropriate download source.
Open Green Wallet on your device.
Select "Create New Wallet" to begin.
Agree the the Terms of service and click on 'Continue'.
Write down the 24 words associated to your wallet on a piece of paper.
Anyone with access to these words can take control of your funds!
Do not save these words on your computer
Do not take a picture or print them
Make sure to write them correctly and in the right order.
Store this piece of paper in a safe place.
Insert the words that are asked of you to make sure that you have noted them correctly.
If any of the words are incorrect, press back to get a chance to look at the words again.
Insert a 6-digit PIN that you will use every time you wish to access the wallet.
Losing this PIN makes you lose access to this wallet. As long as you have the 24 words, you will not lose your funds.
Enter your PIN once more to make sure that you have entered it correctly.
Add a name in order to identify your wallet. You can create multiple wallets within Green Wallet.
Select 'Receive' in order to display a Bitcoin address to use for accepting funds in your wallet.
You can copy this address by selecting the clipboard icon to the right of the Bitcoin address (begins with 3).
You can also generate a new address in this wallet by selecting the rounded arrow icon in the top right corner.