1) The Earth is a planet, which formed as part of our Solar System, about 4.5 billion years ago.
2) The Earth is one of the terrestrial planets (the four planets closest to the Sun, plus the Moon, and the asteroids), which are all made mainly out of rocks. The terrestrial planets are the subject of study of Geology (in the modern definition).
3) All the terrestrial planets formed out of the same materials, and have evolved (changed in a predictable way) by similar natural processes, but each one has unique features. The Earth is the most evolved planet in our Solar System. It is still geologically active and evolving.
4) The Earth is a complex system of interaction between internal processes (volcanism, earthquakes, mountain building) and surface processes (involving water, the atmosphere, and lifeforms). Internal processes are driven by the internal heat of the planet. Surface processes are driven by heat from the Sun.
5) Science is not a body of facts, but rather a method of learning based on observation and testing (the scientific method). Scientific knowledge is continually growing.
6) The study of geology can increase your awareness of the natural world around you, and your general knowledge of science (chemistry, physics, math). It can also increase your knowledge of unexpected subjects (such as language).