expression
A common parting phrase or warning, literally 'attach your attention'. Used when seeing someone off or cautioning them.
気を付けて行ってらっしゃい。
Take care on your way.
車に気を付けてください。
Please be careful of the cars.
The dictionary form; 気を付けて is the te-form used as a set phrase.
From 気 (attention, spirit) + を + 付ける (to attach), literally 'attach your attention'.