A punctuation mark is typed straight onto the word, with no space in front of it. The hand therefore has to produce the letter and the mark in one sweep, and only then the space.
home, time: well-known
The comma and the full stop live in the bottom row, in the columns of the right middle and ring fingers, and need no shift. The semicolon sits on the home row under the right little finger, and the colon is the same key with shift. The hyphen belongs to the right little finger as well.
The question mark and the exclamation mark need shift as well. The usual mistake with them is releasing shift too early, so the unshifted character appears instead of the mark.
The drill gives words with their marks attached rather than marks on their own, which is closer to what real writing does.