I want to understand key functions of powershot S1IS as I do not have manual or booklet.

Yes, Canon offers free of cost ccd imager chip replacement that is reason of no image in camera mode.
Click Canon CCD Imager Advisory for details.

Problem: dust in the gaps near lens which makes it jammed. Effect: the sceen shows blk color. Solution: just blow over it or vaccum it.

If you have an S1 IS, this is likely a very different problem (although symptoms may be the same). This is more likely to be a defective CCD imager. If so, Canon should fix this for you for free, including free shipping both ways. This is regardless of your camera's warranty status. Please check this link for more info.

Applicable cameras include:
A40, A60, A70, A75, A80, A85, A95, A300, A310, S1 IS, S60, S200, S230, S330, S400, S410, S500, SD100, SD110, IXUS V2/300/400/430/500, IXY Digital 30/30a/200a/300a/D320/400/ 450/500

If it is Canon S1IS camera then it has bad ccd imager that need to be replaced to get correct picture. Canon will repair it free of cost.
Click Canon CCD Imager Advisory for details.

go to canon.com look up your model go to users guide and you can look at manual or print it for free.

Try lithium batteries. Sometimes regular batteries even when new cannot run a digital camera.

See this link.

Went to canon website and found they had a problem with the ccd which causes these problems and will fix it for free. Apparently there are lots of models with this faulty component.

go there and you'll see you're not alone !
S2 IS Question: black screen in S1IS canon camera - DigitalCamera-HQ

it could be the battery is at the end of its life. try getting a new battery for it and trying agian. If this is not the case then it could be the camera has come to the end of its useful life (they are not built to last very long sadly) but try the battery and see what happens.