Geostrategy is like playing a game of chess but instead of a game board, we use a map of the whole world! We look at all the different countries and think about their strengths and weaknesses, and decide how to move our own pieces (like military or economic resources) to get the most advantage in the game.
For example, if we want to make sure our country is safe from enemies, we might decide to build military bases in certain parts of the world where we can keep an eye on things. Or, if we want to have more power over the economy, we might try to control important resources like oil or minerals. Basically, geostrategy is all about thinking ahead and making smart moves to get what we want in the big game of world politics.