%spam is a variable that he created. The options are limited when using it the way he used

inc -u60 %SPAM-Wale

When using the variable like this the -uN (N being any number) switch the variable is unset after N seconds. So, in his example:

inc -u60 %SPAM-Wale

the variable %SPAM-Wale will unset after 60 seconds. However, this is a good simple spam protection system. The portion after the On TEXT event

if (%SPAM-Wale) { halt }

will recognize that the variable %SPAM-Wale is set to unset after 60 seconds, meaning since it halts upon finding the variable not null, it'll prevent anyone from using the command for 60 seconds. The 60 can be changed to anything. :)

Hope I was helpful.