To be more exact than an entire reference post, what you're looking for is strPos or striPos.
strPos(%haystack, %needle, %offset) - Case sensitive search, will return position in haystack that needle is or -1 if it is not there
striPos(%haystack, %needle, %offset) - Case insensitive search, will return position in haystack that needle is or -1 if it is not there
function isItThere(%haystack, %needle)
{
if(striPos(%haystack, %needle) >= 0)
return 1;
return 0;
}