I use a card game to help my students grasp the concept. I draw two cards at random and hold one up on each side of my face.
Red cards are negative and black cards are positive.
Tens and face cards are worth ten, aces are one, jokers are zero and all others are at face value. I call out addition, subtraction, multiplication or division and remind the students to go from left to right as they read. They must write the equation and answer while I count quietly to five. The students have very lively discussions over their responses because they must justify their answers. Often the problems lend themselves to good explanation.