Here's some information in English:
http://www.bahn.de/international/vie...bahncard.shtml

Bahn.bonus is simply a point collecting program that can mainly get you some nominal awards (upgrades, bistro certs, etc.) or qualify you for bahn.comfort status (special seating areas on the train, lounge access, etc.).

The BahnCard is a discount card. You can apply online for the non-discounted cards. You can apply for all of the cards at DB ticket offices. You will need a passport-size photo; you will get a temporary card immediately from the ticket agent and the plastic card will be mailed to you.
The BahnCard25 gives you 25% off on DB fares, including those sold at the SparPreis fares, which are themselves up to 50% off. So you could theoretically get 65% off with the BC25 on top of that. However, SparPreis fares tie you to specific trains, are non-refundable, and are highly capacity controlled. For 2nd class, it costs 55EUR.

The BahnCard50 gives you 50% off on all standard DB fares, giving you full flexibility (interrupting your journey--domestically you must complete travel within two days, refunding your ticket, choosing your trains, etc.). For 2nd class, it costs 220EUR. If you are a student (and 26 or under), you can pay half that.

Given that you qualify for the Germain Rail Pass Youth rates, I think that will probably be the best deal for you. That gives you unlimited DB travel within Germany (and to Salzburg) for 4-10 days within a 30 day period, costing $201 (4days) up to $288 (10 days). http://railpass.com/new/passes/pass/germany.asp
DB sells the German Rail Pass in Germany at certain stations, but only in the 5 and 10 day variants (154EUR for 5 days; 204EUR for 10 days for the youth version).

http://www.bahn.de/international/vie...ail_pass.shtml

For you, there is also the Germany-Austria rail pass, which is more expensive, but also has youth rates.
http://railpass.com/new/passes/pass/germany-austria.asp