Side note: someone asked about the picture in my previous post. Specifically, the question addressed the way in which spacing is achieved within the words and the material at the end of the bottom line. The answer lies in quads and spacers (pictured above). Much like kerning and tracking on digital text layouts, there are defined widths used in letterpress. However, working with metal type is more like mortising.
Have I bored you to tears yet? Good. The em dash and the (more common) en dash form the basic units of spacing. For filling larger spaces, furniture and reglets are needed. Typesetting requires careful intent and deliberation...which is why it is such a great metaphor for learning.