各 means "each". It is a prefix: it goes straight onto a noun, with no particle, and says something applies to every member of a group one by one. The noun is usually a kanji word, though a few loanwords take it too: かく各ちいむチーム, かく各くらすクラス.
Several 各 words are everyday vocabulary in their own right: かくじ各自 "each person, individually", かくち各地 "all over, in various places", かくしゅ各種 "all kinds of", and かくえきていしゃ各駅停車, the local train that stops at every station.
各 is formal and written: notices, announcements, instructions, the news. それぞれ says the same in conversation. It is a word of its own, so it takes の before a noun, and it can also stand after the subject.