To setup Braintree you will need:
Your Merchant ID
1. Get your Braintree keys from here https://www.braintreegateway.com/login
2. Click on the settings gear in the top right > then hit API.
3. You will need: Merchant ID, Public Key & Private Key.
4. Copy and paste them into the setup boxes.
5. Click Save.
If you want to accept multiple currencies with Braintree you will need to enable them in the Braintree portal.
You can set up other payment methods like SEPA that you might have enabled on your account.
Address Verification Setting
For AVS you will need to ensure that you have this configured in your portal.