im trying to find out how to play pedal tones. does it have to do with the slides

No, it has nothing to do with slides. It has to do with being loose. Mouthpiece barely touching the lips, lips loose almost like warming up by blowing air out of your loose lips but there has to be some measure of control which you will have to find for yourself with practice.

NO NOT LOOSE.

ask a qualified teacher, I don't use pedal tones because my teacher thinks they are unessecary for me, I you don't do them correctly, it will hurt you. Have a teacher tell you how to do it and see if you are doing it correctly.

Having played the Sousaphone trombone, and base which are much lower in range than a trumpet with correspondingly larger mouthpieces. The lip positions and control through the lips is much exaggerated compared to the trumpet. You can only go so low with a small mouthpiece and only so high with a huge one. My being able to achieve easy and good pedal tones on the trumpet came from the knowledge of how to play these other instruments. This I know your lips have to be loose to vibrate at a slow enough rate to produce the tone. Whether this will help you with anything else is another matter, but it will not hurt you. In fact it helps a fatigued embouchure. A last note, "Don't be afraid TO TRY!! Better to explore and discover than to keep your head and mind buried in the sand of tradition (and misinformation).

GOOD LUCK!!!

Bobby Shew, 1997 "

yes yes, do not be loose! The mouthpiece has to have the same contact at when u play any other note. You also have to use a lot of air just like u are playing a regular note. You cant just relax and let the note come out...you have to actually play it. just start on a low F and go down to a pedal F...F,C,A,F...in that order descending...It probably will sound horrible at first, but I got a hang after about a week, a little longer.