The Coriolis effect has to do with things in motion on something that is rotating. An easy example is imagine standing on a merry-go-round with a friend and throwing him/her a tennis ball. You might throw it straight, but it will curve away from where you aimed because the merry-go-round is spinning.
We happen to live on a big thing that’s spinning, called the Earth. If things are moving far enough, they will curve because the Earth spins underneath them.
Near the equator, the Earth is bigger in its direction of rotation, as shown in the picture above. This means that while the Earth rotates east, things near the equator move faster. Say you’re in the northern hemisphere and you throw a tennis ball (very far!*) north. The Earth up there is moving slower, so your ball lands to the right of where you aimed because where you threw it from was rotating faster than where you aimed.
The same is true if you throw south. In fact, in the northern hemisphere, things will always end up to the right of where they were headed. (In the directions east and west the reason is a little different, having to do with the Earth’s curvature, but the direction is the same: right.) And in the southern hemisphere, the logic is opposite, so things end up to the left.
*You can’t actually throw far enough to see this
