In the winter, the sun is lower all day than in the summer. Then it gets lower again. In the winter, days are shorter than in the summer. Then days get shorter again. To see how the angle of the sun changes during a day and a year, do a demonstration with a globe and a flashlight.
Most globes are on a stand that is inclined at the proper angle.
Here are two diagrams that show how the angle of the sun and the length of your shadow are related. For precise relations between distances and angles, you have to use trigonometry. In the first diagram, the sun is fairly low, and the shadow is long. In the first diagram, the sun is fairly high, and the shadow is short. The table was made using some rather complicated geometry and trigonometry, based on knowledge on the positions of the earth and sun and how they change in time.