how to change git folder from previous to new?

Having problem in using the same repository previously used

I was trying some new stuff with my rails project and ended up losing its major functionalities, but I git my project on GitHub. So i downloaded from there and now when I made some changes to this newly downloaded file, I cant git to same repo now. How to git into that same repository. Like it has 8 commits now and now if I do my another commit it should be the 9th. Any help?

Hope the problem is clear..