SID’s and STAR’s have nothing to do with ILS frequencies. :)
The SID/STAR system (in more correct terminology called P-RNAV procedures) are exactly that, a series of waypoints with or without spesific altitude/speed restrictions, which utilize the plane’s RNAV system (think of it like your GPS).
They are like predefined roads in the sky in and out of airports which helps the controllers by giving a level of expectation of where a plane is gonna be, and it also significantly helps for safety and cost reduction.
A SID’s job is to take you from the runway, to a spesific waypoint which in most places would be the first waypoint in your flight plan.
A STAR’s job is to take you from the last waypoint in your flight plan down to an approach, whether it be ILS, GPS, RNAV, LOC, VOR or anything else. :)
In short, it’s a way to reduce controller workload, but it has nothing to do with radio frequencies. :)