Recognize parallelograms visually by looking for a slanted rectangle. See that kite? It's almost a parallelogram, but the sides don't match.
Pro Tip 2/3
Opposite Angles
Remember, parallelograms have opposite angles that are equal, not just sides. The parallelogram in your drawing should have two angles equal to the ones opposite them.
Pro Tip 3/3
Not Always Flat
Parallelograms can look skewed, not always flat like a square. Your box’s top is a parallelogram because the sides slant.