Basically, Katakana and Hiragana charts are correspondent each other. There are 46 basic Katakana, 25 Daku-on, 33 contracted sounds and some special combinations of Katakana to describe foreign words.
Japanese also use Kanji, or Chinese characters, so that any Japanese text usually contains all three scripts.
Kanji, Hiragana, and Katakana each have different roles in Japanese. The role of Katakana is primarily to transcribe loanwords (words borrowed from other languages) including foreign name. For example, カメラ(pronounce ‘kamera’) for camera, ラジオ(pronounce ‘rajio’) for radio, and トム(pronounce ‘tomu’ for Tom.)
Katakana is also used to write onomatopoeic words. For example, トントン(pronounce ‘ton-ton’) to represent a knocking door sound andドキドキ (pronounce ‘doki-doki’) to represent a fast heart beat. Katakana is sometimes used for emphasis, similar to the way bold or italics are used in English. If you look a Japanese comic book, you can easily find lots of them.