Okay kiddo, imagine you're playing with your toys in your room and your mom calls you to come eat dinner. You know that you're in your room playing, but now you are aware that there is dinner ready for you to eat. That is an example of a change in your awareness context.
Now imagine you're at school and your teacher tells you to do your math homework. You know that you're at school in a classroom, and you weren't thinking about your homework until your teacher mentioned it. That's another change in your awareness context.
Awareness contexts are the different situations we find ourselves in, and our awareness of our surroundings changes depending on where we are and what we're doing. It's important to be aware of our context so we know what's happening around us and how we should act.