I do not have premium account of gitHub, and I want to know If I have private repository and someone do not have paid version of gitHub account, can I let him to contribute with me on private repository, and all of commit and change that done by that public account remain private for my project.
Thanks.
Yes you should be able to add a collaborator to a private repo, GitHub provides steps. Private repos on GitHub require a paid per month subscription. A non paying member should be able to be added to a private repository.