A hacksaw has a metal frame and a thin blade used for cutting into plastic and metal.
Ideally you should hold the hacksaw with both hands.
Grip the handle of the hacksaw with your dominant hand and extend your index finger along the handle so that it points towards the end of the blade. Keep your finger extended when working to help you guide the saw.
Your other hand should grip the opposite corner of the hacksaw frame. This hand is there to guide, but it’s also used to steady the saw, and helps prevent it slipping on the material and cutting off course.