katakana
syllabary used to represent foreign words (non-Japanese words)
The katakana is most often used for transcription of words from foreign languages, especially English. Moreover they are normally used for foreign countries, places and names. For example would my name "Morten" be written as "モルテン" which can be phonetically translated back to "Moruten".
I would recommend to use the same learning methods as mentioned under "Hiragana".
If one takes a closer look at the katakana, you can see that some of the characters look like their hiragana equivalents.
A nice way to learn the kana is to use the LearnKana! applet I've developed at this site for beginners who want to learn hiragana and katakana.