〜たち
plural (people)
Person noun + たち
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Japanese nouns don't change for plural: 本 is "a book" or "books". For people, though, たち marks a group: 子どもたち, "the children"; 私たち, "we"; 学生たち, "the students".
It often means "and the others" rather than a strict plural: 田中さんたち is "Tanaka and his group", not several Tanakas.
たち is for people, and sometimes animals, never things: 本たち only happens in poetry and children's stories.
A rougher alternative is ら (僕ら, "us guys"), and a politer one is 方 (かた), as in あなた方.
Examples
子どもたちが公園で遊んでいます。
The children are playing in the park.
私たちは学生です。
We're students.
田中さんたちはもう帰りました。
Tanaka and the others have already gone home.
友達たちと海へ行きました。
I went to the sea with my friends.
学生たちは教室にいます。
The students are in the classroom.