Why does my nikon d300 take forever to take pictures when the flash is not on?

I'm new to these type of cameras it use to be my uncles but he didn't use it, anyways it takes forever to take pictures but when i put the flash on it is quick i use a VR 18-200mm lens

Because the camera needs time to absorb enough light to get a proper picture. The less light there's, the longer the sensor needs to stay on to get enough light.

It's faster when the flash is on because the flash supplies MORE light than what is available ambient.

The shutter has to remain open for much longer in dim conditions. Unless you have the camera on a tripod, I'm sure you are also getting lots of blurry photos, because any subject or camera movement during such long exposures will result in blur.

Umm… A photography course would be very beneficial to you!

The lens you have - the 18-200mm f3.5-5.6 - is a slow, variable aperture zoom that is best suited for use outdoors on a sunny day. Trying to use it indoors without flash is not going to work unless you use a really high ISO.

Here is a down-loadable copy of the Owner's manual in case you don't have it:
http://www.nikonusa.com/...300_en.pdf

You really, really, really need to seriously read & study the Owner's Manual for your camera, There's no other way to learn to use it.

Knowledge of the Exposure Triangle will also help you:
http://digital-photography-school.com/learning-exposure-in-digital-photography

At this site (which I use and recommend) http://www.calculator.org/...osure.aspx choose the Scene 'Domestic interiors at night, subject lit by campfire or bonfire' and then look at the aperture/shutter speed recommendations for f4 and f5.6 at ISO 100, 200, 400, 800, 1600, 3200 and 6400. NOTE: The shutter speed at f3.5 which isn't shown will be slightly higher in real life but f4 is close enough for you to see the reason for using a higher ISO. This will also show you why a 35mm f1.4 lens or a 50mm f1.4 lens is so desirable for available light photography.

If you're wondering about the accuracy of the above site, I used the Scene 'Distant view of city skyline or floodlit buildings' and ISO 200 for these pictures. Note that I only made one exposure for each picture and since I shot these on film I couldn't see the results until the next day.

100mm @ f11, exposure for 30 seconds.

200mm @ f11, exposure for 30 seconds.