と

and / with

Joins nouns into a complete list ("X and Y"), and marks the person you do something with ("with X").

Readings

How to form it

Put と between nouns to list all of them: りんごとみかん (apples and oranges). It joins nouns only.
Put と after a person to say who you do something with: 友達(ともだち)と映画(えいが)を見(み)た (I watched a movie with a friend).
Verbs that need a partner take と: 結婚(けっこん)する (marry), 話(はな)す (talk with), けんかする (argue with).

りんごとみかんを買(か)いました。

I bought apples and oranges.

友達(ともだち)と映画(えいが)を見(み)ました。

I watched a movie with a friend.

To join verbs or adjectives, use the て-form: 食(た)べて、寝(ね)ました (I ate and went to bed).
と after a clause is a different と: see 〜と思(おも)う and 〜と (whenever).

やand (among others)
Lists a few examples out of more: 本(ほん)やノート (books, notebooks and so on).