You don't have a lot of options, but to make best use of the pop-up flash, I would use the kit zoom, and:
- find a well lit area if possible, and set ISO800 for starters. Be prepared to go higher
- shoot on Av (aperture priority) say f/5.6
- set Custom Function for 'Flash sync in Av mode' to Auto. It's under the Exposure tab. Auto is the default setting on Canons, so it should be already set unless it's been changed.
- in this mode, the camera will drop the shutter speed to balance the ambient light to the flash, preventing dark backgrounds and softening the harsh light from the flash. The danger is that shutter speeds can get very long so although the subject will be frozen by the flash, anything that moves will suffer ambient blurring. Shoot lots.
- if blurring becomes too much, easiest option is to switch the camera to P, which won't allow the shutter speed to drop below 1/30sec but backgrounds will be dark.