Okay kiddo, imagine you have two cookie dough balls side by side on a table. These cookie dough balls are like plates on the earth's surface. Now, imagine you push each ball towards each other very slowly. Can you see what's happening? That's right, the two dough balls are squishing and getting crumpled up!
Well, when the plates on the earth's surface do this, it's called "plate tectonics." But sometimes, instead of pushing towards each other, the plates slide against each other. Imagine instead of pushing the cookie dough balls together, you push them side by side. When you do that, one of the dough balls moves "up" and the other moves "down." That's called a "strike-slip" movement, and it's just one type of plate tectonics.
So, in real life, instead of cookie dough balls, we have actual plates on the earth's surface. When plates move side by side like this, it's called a "strike-slip fault." And when this happens, it can cause earthquakes! That's why scientists study plate tectonics very carefully- they want to predict where and when earthquakes might happen, so they can help people stay safe.