The katakana syllabary is mainly used for writing borrowed foreign words. The Japanese have been using words from other languages for a while now, and even more so durring the technical revolution. Most of the borrowed words are from (British) English, but they have used words from a few other languages like German (ex. arubaito), Portugese (ex. tempura) and others (but I can't think of any more examples right now).
The way they use katakana to make these words Japanese compatable is by attempting to recreate the sound of the original word with the phonetics of the Japanese language.