Grammar JLPT Level N5 - Lesson 20

Structure of 貰(もら)う:

Giver^(*)に + Recipient^(*)は⁽¹⁾ + Object^(*)をもらう

Recipient^(*)は⁽¹⁾ + Giver^(*)に + Object^(*)をもらう

Giver^(*)に + Object^(*)を + Recipient^(*)は⁽¹⁾もらう

^(*) Giver, Recipent and Object are Nouns
⁽¹⁾ が

Details about 貰(もら)う:

もらう is the 3rd verb that is regularly taught together with くれる, and あげる. It is used to highlight that (A) is 'received' by someone. However, unlike くれる and あげる (which are used to highlight that something is 'given'), もらう requires the に particle (or から) to mark the giver, not the recipient. が or は may be used to mark the recipient, as they are the one performing the action of receiving. を will mark the object that is being given.

私(わたし)はお正月(しょうがつ)におばあちゃんからお金(かね)をもらいました。
For New Years, I received money from my grandmother.
彼女(かのじょ)に手作(てづく)りのケーキをもらった。
(I) received a homemade cake from my girlfriend.
（私(わたし)は）今日(きょう)は学校(がっこう)でチョコレートをもらった。
I received chocolate at school today.

In the second sentence we can see that the recipient has been omitted, while in the third example, the giver was omitted. This is a regular occurrence when using もらう, as the receiver is usually obvious, or the 'giver' may not be important to the overall meaning of the sentence.

駅(えき)でティッシュをもらったけど欲(ほ)しい？
I received some tissues at the station, but do you want them?

In this example, the thing that was given is the focus, while the speaker does not consider the 'giver' something that needs to be mentioned. Sometimes, for very simple sentences with clear context, neither the 'giver', nor the 'receiver' needs to be mentioned.