No prerequisites.
Step 1: Choose a name for your connexion (informative).

Step 2 : (Optional) Enter the secret key of your shop. If you are asked for this please continue the steps below "Configuration - access token". Otherwise continue to step 3a.

Step 3a: Click "Connect" or "Authorise" to finalise the connexion.

Step 4a: You are redirected to Gocardless for authorisation. Please follow the process as requested
Proceed with those steps only if you are asked for an access token.
Follow the documentation as specified here: https://support.gocardless.com/hc/en-gb/articles/17144828748444-How-to-create-an-access-token
3b: When the access token generated , please copy the access token and paste it in the expected field.