What hops to choose, and where to use them?

I have tried to search for an answer, but havent really found one on the forum yet, so here goes...
When looking at hop charts, they list the bittering level of each hop, but my question is how do you know when to use each kind. Are higher rated hops meant to be boiled the whole time, so as to impart maximum bitterness, or are they meant to be added at the end of boil to leave flavor and aroma? Conversely when are the lower rated hops for bitterness used? I am hoping there is a general guideline for alpha acid rating and when you generally use it.
I really like hops, but dont want to use them at the wrong times. Are there general rules for when to use high and low AAU rated hops?

Most high AA hops are used for bittering, though there are exceptions. Bittering hops are normally boiled for 60 minutes.

Lower AA hops are typically used for flavor and aroma and are often boiled for 30 minutes or less.

Some hops, like Cascade, are used for both bittering and finishing (flavor and aroma).

There isn't a firm cut off level of AA that determines if a hop is best for bittering or finishing. Other chemical components in the hop also play a role.

Here is a source that describes uses of hops in more detail, its worth a read:
http://www.howtobrew.com/section1/chapter5-1.html

thanks so much for the help!

and to add, some hops are American, others are European.

you can 'swap' hops quite a bit, but if you were going to brew a 'true' German pilsner or Kolsch, you'd need to use appropriate European hop varieties.

Any hop can be used for any purpose. Trying to bitter an IPA with Saaz or another very low AA hop wastes a lot of hops and wort. Some high AA hops (like Nugget and Warrior) work very well as aroma hops, even though they are at the high end for AA; others don't.

The best way to get a handle on hopping is to read a bunch of recipes.

It also depends on what flavors you wish to end up in the final brew. Some hops are fruity, some are spicy, some have a woody flavors, etc. So that influences which hops you wish to use.

I'd suggest figuring out what type of beer you like to brew, whether it be a style of beer or a clone of a certain brand. By researching the recipes online (check the recipe section here, or just google "stone ipa clone recipe", for example). You'll see certain hop varieties pop up again and again - that's a good sign of which ones you'll want to use. If you can't find that specific hop, there are substitute hop varieties listed in websites (Willamette as a replacement for fuggles, etc.)

Sometimes brewery websites even list out their hop and malt varieties which makes it even easier to design your recipe (Red Hook is a good example).

Lastly, use a brewing software to figure out how much hops to use and how long to boil them to reach your targeted bitterness given the specific AA level of the hops you end up purchasing.

Hope this helps.

There are three thing to know about hops.

1. Alpha acid percent

2. cohumulone levels (non-alpha acid)

3. "U" or hop utilization tables. You can use Rager, you can use Tensith, you can use whatever.

NUMBER ZERO IS NONE OF THE SCIENCE MEANS SQUAT NEXT TO THE ART.

Buy a lot of beer and drink it. Buy a lot of hops and brew with them.

For your first three brews use three different hops as unrelated as you can get. In general high alpha hops are for bittering and low alpha for flavor and aroma - BUT - really good beer (Firestone-Walker Pale for instance) can be made with low aplha bittering hops and high alpha flavor/aroma.

Hops is one of things you get to loearn more andmore about as you become a better and better brewer. The good news is hops are cool, and friendly; sort of like dogs. A bewildering array perhaps at first, but once you have the working breeds separate from the hounds and some experience with the spaniels it starts to make a little more sense.

RDWHAHB

BYO has a good hop chart that includes uses, typical styles and possible substitutions.

http://byo.com/referenceguide/hops/