Only is used here to tell someone to do one specific action and nothing else. It restricts what is allowed or expected.
Only touch the button once.
Please only open this door.
Only can describe a noun, meaning there is no other of this kind or group. It tells about one and no more.
He is the only student here.
This is the only book I need.
Only is used to show that something happens in one case but not in other times or places. It limits an action or fact.
I only eat vegetables on Mondays.
She only works during the day.
Only can join two parts of a sentence like 'but' or 'except', mainly in formal or old-fashioned English. It gives a contrast or exception.
She would come only she is ill.
I would help, only I have no time.
Only can act as a pronoun referring to one or some persons or things that are unique or special. It shows exclusivity.
Only a few came to the party.
Only one can win the prize.
Only can emphasize that something is normal or natural and nothing more. It softens or explains a situation clearly.
It's only natural to feel sad.
He is only human after all.
