I have an online system I built for two different companies. They share a lot of the same code base but also have a lot difference.
Currently, I do my development by making changes on "test" websites for the two companies, and then overwriting the files in the "live" websites with the "test" files when they're ready. There are 4 websites in total (1 test website for each company and 1 live website for each company). I don't edit any files locally.
I want to understand how I can do this in GitHub instead. I especially want to understand how I can user the concept of 'Branches' to share code between the two companies websites.
I would like guidance as well as actual help.