how do I add Apple Cash to my new Goldman Sachs apple savings

First you must verify your Apple Cash Account. Please review this support article for instructions.

Identity verification for Apple Card or Apple Cash - Apple Support

Deposit money into Savings

When you open Savings you agree to automatically deposit Daily Cash that you earn into your Savings account. You can also add money to Savings from a linked external bank account or from Apple Cash. 

1. On your iPhone, open the Wallet app and tap Apple Card.
2. Tap Savings account, then tap Add Money.
3. Enter the amount that you want to add, then tap Add.
4. Select or add the payment source that you want to add money from.
5. Double-click the side button to confirm with Face ID, Touch ID, or your passcode.

Money that you deposit into Savings starts earning interest on the day that the transfer is initiated from the Wallet app.

If you transfer money from Apple Cash, the funds are typically available instantly. If you transfer money from a linked external bank account, it will generally take a few days for funds to be available for withdrawal.

Set up and use Savings in Apple Wallet - Apple Support