I can't figure out how to deal with octobercms logistics for git repositories and deployment, normally I don't add core files and vendor folder to git, but add only files that are subject to change in the process of developing and running the application. However, when I clone octobercms from github and then run composer install or composer update, it does not create vendor folder. How do I go about it?

if you have a composer.json file, it should restore the vendor folder

A composer.json file is included when you clone octobercms from GitHub, yet it doesn't restore vendor folder.

Please follow the instructions below for composer install:

https://octobercms.com/docs/console/commands#console-install

You might want to use git for plugins and themes only.

This might help as well:

https://octobercms.com/docs/help/using-composer