key points:
cp [old] [new] copies a file.mkdir [path] creates a new directory.mv [old] [new] moves (renames) a file or directory.rm [path] removes (deletes) a file.* matches zero or more characters in a filename, so *.txt matches all files ending in .txt.? matches any single character in a filename, so ?.txt matches a.txt but not any.txt.something.extension. The extension isn’t required, and doesn’t guarantee anything, but is normally used to indicate the type of data in the file.