When talking about an unnamed person, or a person in general, this word is used. The kanji can look very simple to write and read, but it can be a lot more complicated. 人can be read in many ways, and it looks very similar to another kanji, which is 入 (to enter, insert, anything that refers to entry).
(Images from http://www.winttk.com/)
Ways of reading 人:
Onyomi (kanji character with another kanji character): nin, jin
Kunyomi (kanji character with hiragana character): hito
In addition, the kanji 人is also used as a counter for counting persons. If in English, we count people as “one person,” “two persons,” etc., in Japanese it is almost the same, with a few exceptions.
一人(ひとり/ hitori) – one person
二人(ふたり / futari) – two persons
(n) 人(nにん / n + nin) – for more than two people (use the conventional counters for Japanese numbers; ie. さん、よん、ご, etc.)
Extra: Not sure if this info is true, but it would be really nice if it is.
Source: Binbougami ga! (subs by gg)
Sample phrases / sentences:
Ano hito wa watashi no tomodachi desu.
That person is my friend.
Watashi no kazoku wa gonin desu.
There are five people in my family.
Kono naka ni hitori imouto ga iru!
One of them is my younger sister!