。
I want this camera.
Literal
I [topic-は] this camera [subject-が] want.
Textbook 欲しい example. The thing wanted (このカメラ) takes が as the grammatical subject of the i-adjective 欲しい. 僕は marks the experiencer as topic. Note that 欲しい is restricted to the speaker's own desires in declarative sentences — for third parties you'd use 欲しがる.