The easiest way to prove at home that earth has a magnetic field is to use a compass. The north arrow of the compass is made of a magnetized piece of metal (usually iron or steel), so it will point in the direction of the earth’s magnetic pole (north in this case) even if you change which direction you are facing. If earth didn’t have a magnetic field, the north arrow of the compass would not stay pointing north if you moved it around.

Don't worry if you don’t have a compass at home; you can make one yourself! All you need is a paper clip, a bottle cap, a magnet, and a bowl of water. To help explain the following steps, I recommend watching this video.

Fill a bowl with an inch or two of water.
Straighten out the paper clip and rub one end of the paper clip about 50 times with the magnet (be careful not to poke yourself!). This should magnetize the paper clip, just like the north arrow in a compass.
Place the bottle cap upside down in the water so it’s floating. Then place the straightened paper clip on the floating bottle cap.

And that’s it, you’ve made yourself a compass! If the paper clip was sufficiently magnetized, it should start to rotate as soon as you place it on the bottle cap so it points either north or south. If you bump the paper clip slightly, it should rotate back so it’s once again aligned pointing north or south. In this orientation, the paper clip is aligned with earth’s magnetic field.

If this doesn’t happen, you may need to try magnetizing the paper clip again by rubbing with the magnet more. For the magnet, you should be able to use a refrigerator magnet. And if you don’t have a bottle cap, you can also use a piece of paper or a leaf that can float on top of the water.