If you have a tab, the cursor will jump forward by several character positions. If you have a blank, it will move forward only one character. If you have to ask, put it in. The graders do not normally deduct points for having too much documentation. In contrast, you can easily lose points for not having enough.
Different systems use different representations for line separators.
DOS and Windows use CR followed by a newline. This command reads from its standard input, writes to standard output, and performs simple character changes in the process. The idea is to protect you against accidentally editing a file that someone is working on in a group environment. Unfortunately, cs70submitall notices those files and tries to submit them, which doesn't work because they don't really exist. You can safely ignore these warning messages.