左

How it works

に (to) points out the direction the action heads toward — here 左(ひだり) (left). The verb 曲がる(まがる) (turn) shifts to its て (te-form) form 曲がって(まがって) (turn), which here works as a soft instruction (“turn left”), the kind you'd give while pointing the way. Being plain rather than polite, it sounds casual and direct.