There are a few ways that you can use Trello with Confluence:
-If you have a Confluence account, you can sign in to Trello with your Confluence credentials. Use the 'sign in with Confluence' button on the Trello login page.
-If you're an administrator on a Confluence site, you can set up the Trello application for your whole site. This will allow any user on the site to sign in to Trello using their Confluence credentials.
-You can add the Trello macro to any Confluence page. This macro allows you to embed a Trello board on a Confluence page.
For more information, check out this page: https://confluence.atlassian.com/display/TRELLO/Trello+integration+for+Confluence