if your camera is set on auto, it won't allow special metering modes. you need to get if off 'full-auto' somehow.
as far as 'pattern' goes - most cameras use software to identify objects in the frame to optimize focusing. if it's set to 'auto-focus' it'll use only it's software, won't allow you to do anything else. in full auto mode it'll normally use auto-focus.
try to download some kind of add-on documentation from canon site - based on your camera model. there is usually smth available.
you might also google for reviews on special photography oriented sites - they will often point out some tricks.
