Attention is what you are focused on in the moment. If you are in conversation with someone, your attention is most likely directed towards that person. It’s like a torchlight that you decide to direct to one thing vs. another.
Awareness, on the other hand, determines what things you can notice in addition to the thing that you’re paying attention to. It’s like expanding the radius of the light beam: it is still going to be stronger in the area you’re paying attention to, but it will allow you to see more things.
By expanding your awareness, you become more thoughtful and can respond more intentionally to stimuli, which is a core tenet of Alexander Technique.