/help $istok
Note that you should consider reading the entire "page" that opens when using that /help command as it's all related and the other things on that page will help you understand this.
if ($istok(this is a list of words separated by chr32,%somevar,32)) { do this }
%somevar is what you're looking for. You can also use a var for the first part (the list of words). And you can use something other than $chr(32) [space] for separating the words ... just change the 32 at the end to the correct $chr() for the separating character.