Hi,
please pardon my ignorance as I'm not a developer but my question is fairly simple - my understanding is that there is a repository with Bitcoin core code and a lot of people has access to it (dozens). If somebody commits some change (ie. improvement or fix) who confirms that the improvement or fix is propagated to all the end users? Is it one person? Is it by consensus? Does it have to be unanimous?

I'd like to receive comment from somebody who ever did a contribution to the Bitcoin code or really knows how it works.

Thanks!