To enable the Power-Up, users can open the board menu on the right side of the page, select the Power-Ups menu option, and then click the "Enable" button next to the GitHub Power-Up.
After enabling the Power-Up, users can authenticate with GitHub by clicking on the gear symbol and then clicking on "Authorize Account" to give their GitHub account access to Trello.
Then they can click "Link Your GitHub Account." In the new window, they can click "Authorize application" to allow Trello to access their GitHub account
Once the Power-Up is active, users can access it from the Power-Ups button on the back of any Trello card on that board. Here, they can attach a Branch, Commit, Issue, or Pull Request to their cards. By default, linking GitHub content to a Trello card using the Power-Up will automatically leave a comment
In addition to the GitHub Power-Up, there are other ways to integrate Trello with GitHub. For example, Zapier and Unito offer integrations that allow users to sync Trello and GitHub in a 2-way real-time integration to sync issues and cards