Interesting question! I assume you're referring to the Earth's magnetic field. Well, the first (obvious) answer is that there's a magnetic field that surrounds the Earth - this is what you use whenever you use a compass to find north. A much cooler (and maybe more important!) effect is that the Earth's magnetic field acts as a shield for us! You see, besides the light we see, the sun is constantly spitting out charged subatomic particles. These particles are constantly streaming towards the Earth, and without the magnetic field, they would enter our atmosphere and could cause quite bit of damage to the atmosphere, life on the surface, and our electronic equipment. However, the Earth's magnetic field deflects these particles, and funnels them into the north and south poles of the Earth, where the magnetic field lines enter and exit the Earth. There, when the particles hit the atmosphere, they light it up, creating what we know as the Northern (and Souther) Lights.

So, there's plenty the Earth's magnetic field does for us!