Left hand-radical 扌 (the side form of 手) - the indexing radical. Anchors 按 in the family of hand-action verbs: 拿 (take), 推 (push), 拉 (pull). Here it stages the press: a hand reaching out to apply downward pressure.
Right 安 supplies the sound (ān → àn, just a tone shift) and a faint semantic flavour: 安 means 'settle, place steadily,' and pressing something down with the hand also settles it in place. Phonetic family: 桉, 案 - all on the 安 sound.
