Please explain as best you can (like I'm five) the effects of temperature and length of time on the flavor. Does it vary between hops? Am I getting more bitterness the hotter it is, or am I almost exclusively getting aroma and flavor?
The earlier you add hops in the boil the more bitterness they will impart from the alpha acids (high alpha = more bitterness). Hops added later will impart less bitterness and more of their specific aroma characteristics.
The Alpha Acids in hops isomerize at about 180-185° F. If you put the hops in at flameout, you will get some IBUs/bitterness out of them. If you wait until the wort is 175 or so, you only release the aroma & flavour compounds.
So, once your boil is done, cool the wort to 175-ish then stop cooling. Put your hops in (I usually do 2 - 3 oz), put the lid on and let them sit for 30 - 60 min. Then finish cooling and transfer/pitch/ferment.