彼は老人の背中にそっと手を添えて階段を上った。
He climbed the stairs with his hand gently resting on the old man's back.
先生は生徒の手に自分の手を添えて筆の運び方を教えた。
The teacher placed her hand over the student's to show how to move the brush.
カップは両手を添えて持つと安定する。
A cup is steadier if you hold it with both hands.