When taking indoor photos, sometimes i get shadows

If you're getting shadows on the bottom center of indoor photos when take with a flash, it is most probably due to the length of the lens on the camera.

A long, telephoto / zoom lenses will create the largest amount of shadow, while shorter and wide angle lenses will be least likely cast shadows. You can reduce the amount of shadow in pictures by removing the lens hood that may be on the end of the lens. The lens hood is to primarily to shield the lens from direct (sun) light, and probably isn't needed for indoor flash photography. Also, rely less on the zoom function of the lens on the camera and physically moving closer to your subject instead. The flash will need to provide much less light output and result in more flashes per battery.

You could use a separate flash - held off the camera so that the lens is not obstructing the light of the on camera flash. Using a Nikon Speed Light, you can set the on camera flash to provide a low output, that would be used primarily to trigger a Nikon Speed Light held by someone or arranged on another surface etc. Youtube is a great source for real life, practical "How To" videos for many operations of the camera and accessories.

I hope this was helpful!