が

The particle が is a subject marker in Japanese. It is used to indicate the grammatical subject of a sentence and often places emphasis on what or who is doing something or what exists.

• Introducing the subject of existence

  ねこ猫がいます。

  There is a cat.

• Answering questions with emphasis

  When answering questions like だれが (who) or 何が (what), が emphasizes the specific subject.

  だれがせんせい先生ですかきごう？

  Who is the teacher?
  やまだ山田さんがせんせい先生です。

  Mr./Ms. Yamada is the teacher.

• Describing characteristics or states

  そらが空があおいです青いです。

  The sky is blue.

• Contrasting with other subjects

  が can emphasize one subject in contrast to another.

  わたくし私がいきます行きます。

  I (not someone else) will go.