What to do after cloning repo from git

I am just a git starter, basically I clone a git repository and now I wanted to commit the changes that I made in a file. when I run the command git commit it says not a git repository,

So being a starter in git i just wanted to ask that do i need to run this command first - git init and then git commit? Or in between these some more steps to follow to commit the file?

I need to commit files on Bitbucket.