Ga in a Special Circumstance
The object of the sentence is usually marked by the particle "o," but some verbs and adjectives (expressing like/dislike, desire, potential, necessity, fear, envy etc.) take "ga" instead of "o."
Kuruma ga hoshii desu.
車が欲しいです。 I want a car.
Nihongo ga wakarimasu.
日本語が分かります。 I understand Japanese.