Add

git add .
git add path/to/file.txt
git add path/to/file1.php folder1 path/to/file2.js path/to/folder2
git add ../path/to/file.txt ../../path/to/folder

git add adds files to "staging" for the next commit.

You can remove files from "staging" (basically, undo the git add) like so:

git restore --staged file1
git restore --staged .
git restored --staged path/to/folder1

Official documentation link.