How to generate a hash key?

Hello there, could you please explain the process of generating a hash key in simple terms? I've heard it's a crucial step in cryptography and digital security, but I'm not entirely sure how it works. Could you walk me through the steps, from the input data to the final hash value? And also, what are the key factors that influence the uniqueness and security of a hash key? I'd appreciate any insights you could offer on this topic.