There's so much to learn, but to start with:
Do a search for tectonic plates and learn about plates that drift apart, collide, and slide under another. That will tell you where your mountains, volcanoes, and island arcs go.
Do a search for climate zones and learn about the general rules of what kind of weather occurs in certain areas. That will tell you where your jungles, deserts, forests go as well as where it rains a lot, where there can be lots of fog, where there are hot summers, where there are cool summers, where it snows, and where the big resort hotels go too!
Study the flow of rivers and learn the basic rules:
1) Rivers flow from higher land to the sea. They never go from lower land to higher land.
2) Rivers join on their way to the sea...they don't split.
3) They seldom, if ever, cross continents because the higher land is usually towards the center of the continent.
4) They don't appear out of nowhere. They act as drainage to mountains. Usually, every mountain range will have rivers that eventually join into one big river. For instance, the Mississippi drains the Rockies. The Nile drains Africa (The Congo river too). The Amazon drains the Andes. Notice how everything goes from high to low...mountains to ocean.
Finally, learning as much as you can about history can tell you a lot about the countries that might develop on your world. For instance, I had two countries that were side by side. Their south sides faced the southern polar ocean. The northern coast that they shared faced the warmer sea, plus, just by chance, it had some gorgeous bays for harbors. Don't you think they fought over who gets to have more of the warm coast?
Also, I have two giant continents on one side of the world. Together, they reach almost from the north pole to the south pole. You could sail around them, but you'd have to pass through icy polar oceans that might be passable only at certain times. And it would be a loooong trip. Or you could sail between them BUT there happens to be a good sized island right between them. Later in my world's history, all the other countries joined up to make really big countries, but the island stayed a nation all by itself. Why? Because it would have been able to control the shipping from one side of the world to the other. It could command tribute and tolls, and it would see all the ships, people, and merchandise of the world pass around it. Because of its position, the island nation would be one of the richest in the world.