Illustrator: PEN TOOL 1: Drawing Straight Lines with the PEN Tool

To create this abstract image I practiced drawing shapes with the pen tool and filling them with various colors, patterns, and gradients while adjusting their opacity.

To create this "Paper Airplane" I made the grid visible above the artboard and created several triangles with the pen tool, moving them above and below each other and filling specific ones with black to achieve the overall image.

To create this "Origami Paper Crane" I created several triangles with the pen tool and filled them with the "Live Paint Bucket" feature. I moved the triangular layers above and below each other to make sure the image looked correct.