A routine is a simple smartapp that the company decided to put in a separate section of the mobile app with the idea that many people would only need routines.
Core is a very sophisticated community – created rules engine Smartapp. Popular and much appreciated by power users, but too complex for some people.
Smartthings is very versatile, and there are many different ways of accomplishing the same goal. It’s just that none of it is very intuitive. The following might be of interest.