もらう is the counterpart to くれる and あげる, and it is used to express the action of 'receiving' something. The focus is on the person who gets the item. A key difference from くれる and あげる is how particles are used. With もらう, the giver is marked with に or から, while the recipient (the subject of the sentence) is marked with は or が. The object being received is marked with を.

• 私(わたし)は誕生日(たんじょうび)に友達(ともだち)から素敵(すてき)なプレゼントをもらいました。
  For my birthday, I received a wonderful present from my friend.
• 先輩(せんぱい)に京都(きょうと)のお土産(みやげ)をもらった。
  (I) received a Kyoto souvenir from my senior.
• (私(わたし)は)今日(きょう)は会社(かいしゃ)でコーヒーをもらった。
  I received some coffee at work today.

Notice that in the second example, the receiver was left out, and in the third, the giver was not mentioned. It is very common to omit these elements when using もらう. This happens when the receiver is clearly the speaker, or when the identity of the giver is unknown or irrelevant to the point being made.

• スーパーで無料(むりょう)のサンプルをもらったけど欲(ほ)しい？
  I got a free sample at the supermarket; do you want it?

In the sentence above, the main point is the item that was received, so mentioning the giver is unnecessary. For very straightforward statements where the context makes everything clear, it's possible for both the giver and the receiver to be unstated.

• これをもらったよ！
  I got this!