Katakana works very similarly to hiragana however katakana is used for words that come from languages other than Japanese and Chinese since Chinese words are written in kanji. A good example of when to use katakana is when an English word is being written in Japanese. Katakana like hiragana also has a chart and can easily be memorized using it.

N W R Y M H N T S K
ン(n) A
チ(chi) シ(shi) I
フ(fu) ツ(tsu) U
E
O

The muddied sounds for katakana work the same way as the hiragana sounds do which makes them pretty easy to learn.

P B D Z G
A
ヂ(ji) ジ(ji) I
ヅ(dzu) U
E
O