Our common sense tells us that the Sun gives us light and heat. But the heat from the Sun does not distribute evenly, and that is one of the major reasons why temperature is different at different latitudes. To better understand this, you can go grab a small flash light and a volleyball. Turn on the flash light and aim the light at the volleyball. As you can see, the brightest spot on the ball will be the place closest to the flash light. The situation can be shown in the picture below:

In fact, the same thing happens to the Earth. The equator on the Earth is the closest to the Sun all the time, and that is why the equator area gets the most light and heat all through the year, Due to the fact that the Earth tilts on its vertical axis by 23.5°, and the north end of the axis always point towards the North Star as the Earth revolves around the Sun, we get season changes. When it is Winter in North Hemisphere, it is then Summer in South Hemisphere. That is why Americans celebrate Christmas in the snowy winter while Australians celebrate Christmas on the beach enjoying the summer sun shine. You can also refer to the picture below to understand better: