손발이 잘 맞다: click, be hand in glove, be very cooperative

손발: hands and feet

잘 맞다: fit on, fit together, hitch, click

→ To be 손발이 잘 맞다 means your hands and feet cooperate well when you do something. When we say 손발이 잘 맞다 with someone, it means you click with someone, you’re very cooperative with someone – you have a very good chemistry between/with someone