GitHub uses an additional layer of security to control access to repositories it hosts.
Your username and password let you login to GitHub using a web browser.
Each individual application on your computer – like Xcode – need their own separate “secret” that allows that software to access GitHub. This secret is called a token.
Please follow this link to create your token.
TIP
Really. It’s important that you actually click the link above… ⬆ to create your token.
Then, follow along with this brief 2-minute video to finish connecting Xcode to GitHub: