How do I redeem Trello Gold credit?

You can can invite others to Trello at https://trello.com/recommend. If someone accepts your invitation, you'll receive Trello Gold credit (up to 12 months).

To redeem the credit, navigate back to https://trello.com/recommend. From there, you can click the "Start using Trello Gold" link that should appear:

Click this to redeem the credit.