How to add script

RouterOS Scripting
1

Hi all,
I saw some script but little confused, with this types of script

:local interface “wlan1”;
/interface wireless monitor $interface once do={
:local signal $“signal-strength”;
:local snr $“signal-to-noise”;
:local noise $“noise-floor”;
:local thruput $“p-throughput”;
:local freq $“frequency”;
:log info “SNR: $snr Signal $signal Noise: $noise , thruput: $thruput , freq: $freq MHz”;
};


How to write, in /system script, or some where else, How to run this. Or it run automatically