Standard input is what you type into the terminal from the keyboard. Standard output is what appears on the terminal as output from commands, programs, etc.
Standard error is the diagnostic output which also appears on the terminal.
It means to take input from somewhere other than the keyboard, eg. Errors normally appear on the terminal screen, even if the standard output has been redirected to a file. Parentheses define a command environment in which a series of commands may operate within a subshell, without changing anything in the current environment, eg.