I've recommended https://learngitbranching.js.org/ to so many people. Something about seeing it visually, with the arrows pointing from child to parent, just clicks in the mind where a written explanation doesn't. (Not for everyone, of course: some people understand it quite well from the written explanation. But if your coworkers who don't grok Git are visual learners, https://learngitbranching.js.org/ might be the thing that helps them unlock a deeper understanding of what's going on with branches and HEAD and so on).