"command"
Will start that command in the foreground. All output (standard/output) will be shown.
"command &"
Will start that command in the background. All output (standard/output) will be shown.
"command >/dev/null &"
Will start that command in the background. Only error messages will be shown.
"command 2&>/dev/null &"
Will start that command in the background. No output will be shown.
"command >myoutput 2>myerrors &"
Will start that command in the background. Standard output will be placed in a file "myoutput" and errors in a file "myerrors".