This is how you do it:

git stash save "my_stash"

Where "my_stash" is the stash name.

Some more useful things to know: All the stashes are stored in a stack. Type:

git stash list

This will list down all your stashes.

To apply a stash and remove it from the stash stack, type:

git stash pop stash@{n}

To apply a stash and keep it in the stash stack, type:

git stash apply stash@{n}

Where n is the index of the stashed change.