Connecting a GitHub repository requires installing the GitHub App. The in-product flow walks you to the installation button, which then redirects you to GitHub to authorize access.
From the repositories page, click Connect GitHub Repository to open the connection modal.

In the modal, locate the Install GitHub App button. If no GitHub App is installed yet, this is the primary action shown. Clicking it redirects you to GitHub, where you authorize the app and select which repositories to grant access to.

Prerequisites
- Access to the repositories area in your team workspace