Many commands, like ls to list the contents of a directory, can take arguments. This means that you can put something after the command that narrows, expands, or changes the output. Not all commands require switches or arguments. The asterisk matches any number of characters, including no characters. Microsoft's DOS borrowed these from Unix, so you may have seen them before.
Standard input is a file from which a program can receive input.
The default is usually the characters you type on the terminal screen. The default is usually the terminal screen. Standard error is a file to which a program can send errors. The default is usually the terminal screen. Unix often assumes that you know exactly what you want to do, and will at times happily overwrite existing files when you redirect output to them, copy to them, etc.