が (ga) — Meaning & Examples

が marks the grammatical subject — the thing that performs or experiences the action or state. While は marks the topic (what you are talking about), が marks who is doing it.

New information:
が is used to introduce new information or to answer "who?" or "what?"

だれが きましたか？ — Who came?
やまださんが きました。 — Yamada-san came.
(が is used because "Yamada-san" is the answer to the who question — new information)

With adjectives of emotion and ability:
が follows the thing that is liked/wanted/can-do etc:
にほんごが すきです。 — I like Japanese.
みずが のみたいです。 — I want to drink water.
えいごが はなせます。 — I can speak English.

Existence:
えきが あります。 — There is a station.
ねこが います。 — There is a cat.

が with subject clauses:
あめが ふっています。 — Rain is falling.
(The rain is the subject of the action "falling")