If you started doing some code modification but you realize that you should have done these modifications in a branch instead of directly into the branch you did the modification, you can move all files into a new branch. The command is checkout with the parameter -b which create the branch if this one does not exist.
git checkout -b NewBranch git add .
The git add . simply add all uncommited file into the staged area.
Other possibility exist like using git stash to move uncommited code into a temporary place and unstash into another branch.
git stash git checkout NewBranch git stash apply