"Unfortunately many Radio Shack people have little or no knowledge of scanners or radio systems."
At Radio Shack you have questions, we have blank stares. Translation: don't ask questions.
"Triple Trunking simply means it will trunk track 3 types of systems, Motorola, EDACS and LTR. Vacaville uses this Motorola system."
There's where you start understanding.
I'll keep it simple and nonspecific to avoid confusion starting with terms you will encounter. Frequency or channel refers to the radio frequency (RF channel), there are several in a trunked system to allow frequency hopping. Talk group refers to a virtual "sub-channel" within the frequency group, that is the group of RF channels the system uses. Trunk tracking refers to following a talk group as it hops through the RF channels. As a telephone trunk line puts many conversations on a single line a trunked radio system puts many talk groups on a single system using fewer RF channels than a conventional system that puts them one on one using more RF channels.
Now that we know how it works it all comes down to programming. Like a conventional system you can program what you want to hear or program everything and lock out what you don't want to hear depending on when you want to hear it. In any case alpha tags (what you name the channel or talk group) are to eyes what voices are to ears, they help you know what you're listening to. That takes care of the talk groups, how you program the RF channels depends on how your scanner handles control channels. With some scanners all you need are the control channels, with others you need all of them.
That's about as specific as it gets here, for details consult the scanner manual. Don't ask ME what scanner to buy, I'm not an encyclopedia, more like a Rat Shack employee in THAT department. OK, ask away, I'm sure somebody can help you but when it comes to advice around here I hope you're wearing waders and have a shovel handy, EVERYBODY has his own opinion. (;->) Oh maybe it won't be a problem for the experienced, the name of the place where you live translates to village of cows. <groan>
(ducking)