Imagine you're playing a game of tag with your friends, but instead of running around, you're both sitting still on a playground. You and your friend are facing each other and you want to tag them before they tag you.
Constant bearing, decreasing range means that no matter what happens, you and your friend will always be facing each other and moving towards each other, even if you don't move from your spots on the playground. As you get closer to your friend, the distance between you two gets smaller and smaller.
It's kind of like when you're riding a bike towards a tree in the distance. Even though the tree may look like it's getting bigger, it's not actually moving, you're just getting closer to it.
In things like navigation or military operations, it's important to understand constant bearing, decreasing range because it helps people predict where they'll end up in relation to the other person or thing they're tracking.