Check this site for information: http://www.troublecodes.net/Subaru/
I would bring it in, because you can never be sure
Belt was probably installed incorrectly. Take it back and have them check it.
Above the gas pedal, under the dash, there is 2 wires with clips that you plug together. Check engine light will flash the codes recorded in the ecu.
You need an OBDII computer a) to read the reason for the check engine light, and b) to reset the error code if you know what caused the light to come on. If you don't fix the condition that caused the light in the first place, it will probably occur again.
your engine is stuffed
yes
A flashing CEL means a serious problem, not just a warning. Get it read asap. You might not even want to drive it there.
With the proper scan tool.
why the engine light of my subaru came on after i washed the engine
the very top left of the speedometer area.. Mine stays on all the time and still passes emissions. Same year. 200,000 miles and going strong.:)
Not necessarily.