You might think of it like this:

Your house has lots of closets for storage. They are small and shattered out in many rooms. Many closets are full and you have trouble finding things. It would be great to have a magical 'master door' that allows you to put things in the 'master door' and, by magic, your things are automatically placed in the closets in an organized way. PLUS, when you want to get something out of your closets, you simply ask the 'master door keeper' to get the item and they find it for you and keep the closets clean and neat.

Logical volumes and logical volume managers provide this kind of service for disk partitions (closets) and data (stuff you put in closets).