Basically it has the same phonetic sounds as Hiragana, it's just that the characters that represent them are all different. Katakana has sharp edges while Hiragana has rounded characters. Katakana is only used to represent words from a foreign language.
For example:
Let's go through first the Katakana characters:
For example:
グラフ
gurafu
(graph)
ゴルフ
gorufu
(golf)
アメリカ
Amerika
(America)
Since Katakana characters are very limited, foreign words do not sound equally the same in Japanese. So katakana will surely be a challenge for us foreigners of the Japanese language. I sometimes cannot understand how those words ended up like that. lol
