Many people who could be described as experts frequent the site--for example:
https://stackoverflow.com/users/588267
Also: the site's 2018 community survey suggested that about half of the users have a bachelor's degree, and about 25% have a master's degree or higher (out of about 94,000 survey responses):
https://insights.stackoverflow.com/survey/2018/#developer-profile-educational-attainment
The survey also indicates that a large number of users are self-taught, so the site's karma/reputation system also acts as a useful indicator.
As a resource for learning Git, Stack Overflow can sometimes have a habit of presenting complex answers to simple questions and vice verse, and is no substitute for properly curated and differentiated tutorial content.
Stack Overflow's tagging system makes it easy to search for/ learn general things about a concept. It's even possible to search multiple tags (up to three) at once, like this: https://stackoverflow.com/questions/tagged/language-agnostic+data-structures
Many employers consider Stack Overflow reputation to be an authoritative or semi-authoritative source about the quality of a person's coding. Learning Git with Stack Overflow can help with learning Stack Overflow processes and best practices which could help land a programming job once you're ready to start answering questions and really begin racking up enough points to get the prizes.