Lucy, you probably need to shoot in manual to get the correct exposure indoors. As far as what ISO, it depends on how much light there is. You really need to have about 1/400th of a second to get a sharp shot. Open your lens up as far as it will go, meter it on something that is fairly close to grey and set your manual exposure(ISO/shutter speed/aperture) where you want it to be and where it says you have a proper exposure.

Most of the time in places like that I am at 1600+ to get the exposure I want