Hiragana = Alphabet used for native japanese words.
Katakana = Alphabet used for foreign words, country names, foreign places, and foreign personal names.
For example to say good morning "おはようございます". It's a native phrase so you would spell it with Hiragana.
America is foreign word so Katakana is used. Amerika (アメリカ).
I don't believe it matters which alphabet you learn first. I learned Hiragana first.
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Flash cards are great. While I was living over there I used these cards: http://shop.whiterabbitjapan.com/jap...lashcards.html
They are laminated and very durable. That White Rabbit website has lots of great learning materials.