I know that this is a basic question (I am new to cryptography), but how do you figure out the spacing system? Is there one word to a line or do two gaps constitute a space? I am a little confused because I initially thought that there was one word to a line, but then I got to the bit where it says H_ _SW (if you read it vertically). Why have two spaces instead of one and how do you go about figuring out the spacing system?

Along the same kind of lines, how do you work out how many letters are used to represent each of the letters in the original message?