The section you've highlighted in your screen capture is for your library. Typically, that section would be used install Analytics plugins or fire other non-adobe code.
I wouldn't suggest putting code to send s.t or s.tl calls in that section since that is what the rules are for. You can use page load rule or event based rules to set variables and send s.t or s.tl calls. We've got some great information on community YouTube channel that goes over the basics of DTM.