The word "grasp" has two primary meanings. First, it means to take hold of something physically with your hands or fingers, like gripping or clutching an object firmly. Second, it means to understand something, especially something complex or difficult. When you grasp an idea or concept, you comprehend it fully or have a mental hold on it. This understanding can apply to concepts, opportunities, problems, or subjects. So, "grasp what it's all about" means to fully understand the essence or main idea of something.

In a figurative sense, grasping knowledge means having it in your possession mentally, enabling you to use or apply it confidently in life or work. Thus, to "grasp what it's all about" is to acquire a clear and thorough comprehension of the core meaning or significance of a topic or situation.