Set it in "P" mode - this will set aperture and shutter speed automatically.
For moving objects, you can use "S" mode and set a high shutter speed (1/800 and above).
I would also recommend you shoot RAW + JPEG so that you have immediate results with the JPEG files, but you retain the option to re-process your shots using RAW in the future (using an application such as Lightroom or similar).
Please note the S90 will work best when it's bright (e.g. when you're outdoors during the day). For indoor photography in low light you will probably get results that are quite grainy, unless you use flash.