If you want to create a branch from the current branch
git checkout -b {your_local_branch_name}
For creating a branch from a remote branch
git checkout -b {your_local_branch_name} origin/<remote_branch_name>
After editing the files
git add -A or git add <each_file_names>
git commit -m 'your commit message'
git push -u origin <your_local_branch_name>
Which basically add, commit and pushes your file
For updating
git pull origin master
For more information please go through the following tutorial to get more info about git: