To stash a section of your script, first select it by highlighting it, then click the stash icon.
There are a few shortcuts to make using the stash seamless:
option+backspace(on a mac) or
alt+backspace(on a pc) will add your selection to the stash without a title
shift+option+backspace(on a mac) or
shift+alt+backspace(on a pc) will add your selection to the stash and automatically prompt you to enter a title.