[noun] + がほしい
Conjugation (い-adjective):
Polite forms:
The structure がほしい is used to express that the speaker wants something (a noun). The desired item is marked with the particle が, and ほしい is an い-adjective meaning "wanted" or "desired."
The thing you want is marked with が, not を. Since ほしい is an い-adjective, it conjugates like one:
Present: ほしい / ほしいです
Negative: ほしくない / ほしくないです
Past: ほしかった / ほしかったです
Past negative: ほしくなかった / ほしくなかったです
Like other expressions of desire in Japanese, がほしい is primarily used to describe the speaker's own wants. You cannot directly state what a third person wants using ほしい in declarative sentences. To describe what someone else wants, use ほしがっている or report it indirectly with ほしいと言っている.
However, you can use ほしい when asking someone what they want:
がほしい is used when you want a thing (noun). When you want to do something (verb), use 〜~たい instead.