I never had the OE stereo in my truck, cause it had an aftermarket head unit when I got it, which I upgraded to a nicer one, but I would assume it's just like any other car radio I've ever used. Just tune in to the station you want and hold down the numbered button you want it preset to.
"If you ain't breakin' stuff, you ain't drivin' hard enough"
Yeah, 95_318SLT is right. Stock radio just go to the station you want and hold the button down for the preset to register it. You can put two presets per number. Hit it once when you want the first station and twice for the second.