I have to do a little bit of interpretation here since there are a lot of shapes and structures on the surface of the Earth. There are also different layers within the Earth that have different shapes and structures.

Let's start by picturing the Earth if you cut it in half as in this picture. There are different layers. It has a solid inner core, a liquid outer core, and a sort of hot, moldable plastic called the mantle. The outermost layer of Earth is the crust, which is solid and brittle (it breaks instead of bends). The crust is like the graham cracker on top of a roasted marshmallow. The graham cracker (crust) can break and the marshmallow (mantle) can flow.

The inside of the Earth is hot. Very hot. There are radioactive elements decaying and producing heat and all the pressure pushing in toward the core from gravity produces heat. This heat makes convection currents in the mantle that causes the crust floating on top of it to move around too. Sometimes the pieces of crust (aka tectonic plates) move away from each other, likeat a mid ocean ridge, or sometimes the pieces of crust run into each other. When the pieces of crust (tectonic plates) run into each other, mountains form. Another way to make mountains is for the mantle to melt the crust at a hot spot and erupt as lava. The lava cools on the surface and eventually makes a mountain. There are some other ways to make mountains and topography on the crust, but these two are the most common.

Now that we have mountains (topography), we can erode them to make all kinds of shapes. The rock that the crust is made up of breaks down into smaller pieces over time, this process is called weathering. Once the rock is weathered, water can pick up some pieces, called sediment, and transport them until they settle down. Sometimes they move far, sometimes they don't. It all depends on how steep the area is and how much water is moving that is able to carry sediment. Funny thing, the water actually doesn't do the erosion, it's the sediment in the water that grinds down other rocks and causes more erosion. Think of running water over your arm compared to rubbing sandpaper on it. The sandpaper does much more work. Since water flows downhill, it can create channels (aka streams and rivers). These channels keep eroding downward through time. Along the sides of the channels, the hillslopes get steep and more pieces of sediment fall into the channel where it can be transported until it settles down. Eventually, sediment makes it out to the ocean.

The shape of the hills tells you how fast sediment is being transported off of them. Very steep cliffs with bare rock = very fast. Rounded and rolling hills with soil and plants = very slow.

Water isn't the only thing that moves pieces of weathered rock and shapes the landscape. Wind can too. Sand that gets picked up by the wind makes features like these. Dunes.

Where there are no mountains, and no loose sediment, things are pretty flat. Like Kansas.

There are many other factors that alter the shape the Earth, like glaciers, plants, animals, and humans! But, wind and water are the two primary ways that pieces of rock get moved around to produce the shapes you see when you look out your window.