The stash stores snapshots in the same way that commits do. You can see the contents of the stash with
git stash list
You can reference those snapshots with the stash@{N}
notation or use the hashes shown. You can use any of Git's commands that work on commits on stashes. For example
git diff master stash@{0}
will show you what the most recent stash would add/remove to the master
branch if you applied it there.