Katakana, very similar to Hiragana, is also a phonetic syllabary alphabet. Working exactly the same as Hiragana such that, aside from the vowel characters representing: a, i, u, e and o, each symbol is a consonant plus a vowel. An example of a string of these might be: ka, ki, ku, ke, ko (see chart below for symbol counterparts). The symbol above is "ka" in Katakana. Katakana can be distinguished from Hiragana quite easily from its characteristically sharper edges, with hiragana appearing much more rounded and smooth in comparison.
Where is Katakana used?
While similar in appearance and functionality, Katakana and Hiragana are not used in the same contexts as each other at all. Katakana is not used for grammar or Japanese words like Hiragana is, but rather primarily used in order to represent foreign imported words in the Japanese language, and is as such nested in sentences similarly to Kanji. These words largely come from English, Portuguese, German and French. One other interesting and unique usage of Katakana is its usage for Japanese onomatopoeia, "perapera" or "ペラペラ " which means essentially to be fluent or well-spoken is one such example of this onomatopoeia, intending to mimic the sound of speech. Japanese has an extensive array of different onomatopoeia which while rarely used in polite Japanese, are often used in everyday spoken language, adding some flare. That being said, the important usage of Katakana you should prioritise remembering now is its usage for imported words.
History of Katakana
Like Hiragana, Katakana was also derived from the Chinese characters "Man'yōgana", simplifying them. Interesting to note is that the "Kata" in Katakana literally means partial or fragmented, as Katakana is a shorthand representation of the Man'yōgana symbols they hail from, often only reproducing one of the components of the symbol. Katakana was developed around the 9th century by Buddhist monks in Nara in order to translate works of art and texts from India. Originally even as Katakana began to see more generalised use, it was largely used only by men and in official documents, which Hiragana was never used in.