there used to be a book that i would consult for those kind of problems all the time. in america it's called "fowler's modern english usage" and in britain it's called "the queen's english." i guess web look-up sites have probably destroyed the business ecology of reference books with all these simple web look-ups. although i do believe professional writers still consult style manuals like the "chicago manual of style."
the one i could never figure out was why americans write "a hotel" and britons write "an hotel." the answer is that britons don't pronounce the letter "h" in hotel and whenever the leading h in an english word from french is silent, one uses "an" instead of "a." as in "an herbal remedy."
i hope i haven't bored you to death dearie!
regarding "effect," it's the opposite of "cause." and "affect" is how you feel in the morning before you take your meds.
ta ta,
pi