少 has the major meaning of "few/little."
e.g. I have a little money. - I have 很少 money.
Simple.

Then, it is understandable that 多少 means "how much" according to its literal meaning of "how few/little."
Just one step further, and you can the idea.


The meanings of 多, 少, and their combination can be varied depending on the context as I said. You will get the feeling.