Biology is defined as either the science of life or the study of living things. There are many disciplines which fall under the umbrella of biology. To name a few, these include botany (the study of plants), zoology (the study of animals), cellular biology (the study of cells and how they work together to become living organisms), and ecology (the study of how living creatures survive in their environment).
To give you more insight into biology, I'll give you a few examples of what you could end up studying as part of a biology course. First, you could be asked to examine an amoeba as an example of a unicellular organism. Secondly, you could be asked to look at a rock pool and examine how the creatures that live in it cohabit. Thirdly, you could be asked to consider the concept of symbiosis (how one animal will use another animal to its benefit while giving a reciprocal benefit). Fourthly, you could be asked to look at a particular plant and examine how it is well-suited to its environment.
I could carry on writing examples all day, but the most important thing to understand about biology is that it encompasses any study of living things—human, animal, or plant.