Understanding my Flash for my Nikon D3000?

I just purchased a Nikon D3000 along with a flash Model would be (sunpak digiflash 2800) I'm just learning how to use both devices, I've always been pretty much into photography this is my first SLR so I'm quite excited. However I went to a church to take some photos and I could not get my flash to work… It shows some numbers on the back of it, is there a certain way to use these items. I purchased it to take brighter photos but I can't do that If I can't get the flash to work. Please note I'm not nor trying to be a professional I just want to utilize these items to best of my ability. If anyone knows what these numbers signify or if I should have my camera on a certain setting I'd greatly appreciate any Input.

I'm not familiar with your flash, and I'm not interested enough to download a manual, so I'm going to speculate.

But with your description of numbers on the back, sounds to me like you perhaps have a manual flash. Or if it is not a manual flash, perhaps you have a flash not made for Nikon.

In the old days, when using a manual flash, cameras were also manual exposure control. You had to set the camera to 1/60 sec. Then on the flash, set it to the ISO of the film you were using. Finally (and there was sometimes a wheel to do this), you would set the wheel to the distance the subject was at, and the flash told you where to set the aperture.

The wheel did not change anything on the flash - it just was a mechanical "calculator", to figure out the aperture.

These days, cameras have intelligent flash systems. Nikon's is called iTTL (intelligent Through The Lens) metering. But if you buy an aftermarket flash, it must understand iTTL for it to work automatically.

Otherwise, you are back to the manual process I described above.

You generally do not do yourself any favors by buying 3rd party flash units. A flash is the one time you should stick to camera-brand equipment. Yea, $350 seems a lot for a Nikon flash, but if you had one, you would not be having any problems.

You did buy the version that works with Nikon, right? They have a Canon version, that won't work on Nikon.

You have put the AA batteries in correctly and verified that it works manually, right?

You are firmly putting it in the hot shoe, right?

Looking on page 200 of your manual, you need have the flash mode in anything but "not flash" (a circle with a diagonal line running through a lightning bolt), then in any camera mode it should flash. If it doesn't, and after reading the Sunpak manual, you may need to return it for another one.