Team work with GIT and project files. Do not exclude?

Question

git

Recently I began to study git closely, I studied a lot of things. But one thing is not clear. Here, kernel files are added to exceptions, for example, the bitrix/ folder. The developer has arrived. Downloading the repo. AND? Nifiga will not work locally without this kernel. Bitrix is ​​just a particular example. On other CMS the same nonsense. How to be? Upload all project files to repo? (well, except for all sorts of photo banks)

Answer 1

It should be possible to somehow install everything you need.
In the case of Bitrix, you can download and deploy the demo version. But, of course, due to the fact that Bitrix is ​​five years behind the whole php world, it is easier to store the entire core in the repository.
On normal systems, all external dependencies are described in composer.json.

Answer 2

If what is in the folder is present in another git repository, there are git submodules. Otherwise - just store in the git itself.