Nikon D3000 help? Just bought a Rokinon Digital 8mm F/3.5 Aspherical Fisheye Lens for it?

I have set everything to manual, raised the ISO setting, yet my pictures are still coming out dark and splotchy. You can't see anything. Also, I'm unable to zoom in and out with the focus ring. Please help, I'm fairly new to all of this, really was looking forward to getting a new lens for my camera, and now, it doesn't work. :'(

Added (1). Also, how come the flash is unable to release when using this lens? Even when I attach my new flash onto my camera with it it says the flash is in T.something mode, and that I need to change it's settings. What should I do. Sorry if I sound like an idiot, still trying to figure all this out.

If your pictures are coming out dark, it is because A. Your aperture is not large enough, or B. Your shutter speed is not slow enough, or a combination of both.

the Rokinon fisheye lens is not a zoom lens, it is a standard lens, meaning the focal length will always be 8mm. The focus ring is for focusing only.

Now I can't speak from experience of having a Rokinon lens, but I do have a cheaper aftermarket fish-eye+macro lens that screws into a 67mm thread. If I don't have a LOT of light the pictures come out dark and dreary looking. You need a lot of light, and I do mean a lot!
Make sure you have a wide open aperture, high(ish) ISO and a slow shutter.
That'll save a lot of aggravation with the lens.
8mm, as was stated before is 8mm. All fish-eye lenses are a fixed focal point. You can FOCUS with the focus ring only.
remember the lower the aperture # the more light gets in. F/3.5 is a fairly fast lens. The worst problem with fish-eye lenses is that for a great fish-eye effect shot, you need to have the aperture closed, and should be a f-stop of about f/8.0 or so to get a decent fish-eye shot, or up to f/15. Any higher and very little light is passing through. You will need a ton of light for f/8.0 (around 8am to 9am) and f/15 you'd need to have the sun at its full zenith, around 12:30, 1:00PM.
Although, this can be adjusted by using a higher ISO and slower shutter.

You should go with Nikon 55-300mm f/4.5-5.6G ED VR AF-S DX Nikkor Zoom Lens for Nikon Digital SLR

5.5x Telephoto Zoom lens
Nikon VR II Image Stabilization; Tripod Detection Mode
HRI (High Refractive Index) Lens Element
2 Extra-low Dispersion (ED) Elements
Exclusive Nikon Silent Wave Motor (SWM)

Well, if you refuse to read your manual and learn about photography then this will be a challenge.

There's no zoom on it, just a focus ring to, as the name implies, focus.

Take it outside during the day, set camera on iso 400, shutter speed 1/60 and start with the aperture wide open. Now see which aperture you need to get a proper exposed picture.