This may seem a really basic question but search as I might I cannot find an answer that gives it straight.
I have a 450D and a 430EX II speedlight. If I shoot in Av mode outdoors in daylight do I need to AE lock on the background every time. In what sort of situation would I benefit from using AE lock. This leads to a second question with the 450D if I try to use AE lock when the flash is attached (eg focus, AE lock background then recompose) the camera says I am using FE lock. What is the difference between AE lock and FE lock. I am pretty sure I need AE lock for fill flash does anyone know how I lock AE when the speedlight is mounted on a 450D.
And finally the easy solution would be to use P mode so why does this seem to be frowned upon. Are there situations when P mode will not cope?
Sorry for the rapid fire questions but it is driving me mad at present I want to to get the very basics of using fill flash and then start to experiment when I am confident with the basics. I thought about asking on POTN but I have a feeling I would come away with a shopping list for £20,000 of lighting equipment a top of the range DSLR and an inferiority complex about my meagre equipment. Having sold the cat, the my liver and my Wombles albums to obtain the POTN starter kit I still would not have a clue where to begin so please treat my questions as you would an 8 year old