Ah yes, the howler and the sounds it can make. Nothing like doing a set, and you start with a lone howl, and they howl back telling you where they are. Using a howler is catching on, but it doesn't always make calling them any easier. I think you'll hear Randy talk about the use of the howler and later in the season is when it works the best. And it's the truth, come late Feb., that's about all you will need, as long as you don't over use it in your calling areas before then.
And Idaho Hunter, it's true you can use a howler to locate coyotes, BUT, if you stop your vehicle, howl, and a coyote or two howls back, or doesn't for that matter, then you get in your vehicle and drive off, don't ya think that you'd be giving away your tricks to them. It's better for you to go into an area that you suspect has coyotes, wether you have seen coyotes there or seen sign that they are around, and set up to call them, just like you normally would, then use your howler. They will come to just the howl, if you say the right "coyote language". So, use it like any other call, set up in your spot, plan on staying there for at least fifteen minutes, you can do a lone howl or greeting howl, and then if nothing shows, go to your distress sounds of what ever flavor you like. This way, any coyote in the area hears your howl, thinks there is a strange coyote there, and may come to check you out, but then if it hears a screaming rabbit/rodent, then it thinks the stranger just caught lunch and it wants in on the action. Just driving around and howling may tell you where some coytoes are, BUT, just becuase they can hear a howl, even if it sounds right, does NOT mean that they will howl back. Even when you are set up to call and use it, they may just show up with out answering back, BUT on occasion they will, and that is the most exciting calling, is when you howled, it/they answered, then you continue calling and get them to come in. Nothing beats that in the calling world.
Hope that helps a little. Good Luck!!
By the way, there are many different coyote vocalizations, and learning every one isn't necassary, but if you can learn the lone howl, the ki-yi, the female greeting howl, and challenge howl barks, they are most often used.