The main idea is
Stash the changes in a dirty working directory away
So Basicallly Stash command keep your some changes that you don't need them or want them at the moment; but you may need them.
Use git stash when you want to record the current state of the working directory and the index, but want to go back to a clean working directory. The command saves your local modifications away and reverts the working directory to match the HEAD commit.