If you want to add blank space into your document use the \vspace{...}
command. This will add blank vertical space of a height specified in typographical
points (pt). For example, \vspace{12pt} will add space equivalent
to the height of a 12pt font.
1. I can understand this command makes some space in the document, like empty lines. But what's the exact meaning of "space equivalent to the height of a 12pt font"? I can only understand the space equivalent to one line, two lines, or three lines...
2. When do you use this command in your work? Can you give me an example?
Many thanks in advance!