僕は脚本家で食べていく決心をした。

。

I decided to make a living as a screenwriter.

Literal

I [topic-は] screenwriter [by-で] eat-go [resolve-決心] [object-を] did.

脚本家 (きゃくほんか, 'screenwriter') — 脚本 ('script') + 家 (professional suffix). 食べていく ('to make a living' — literally 'eat and go on') uses ~ていく for continuing into the future. 決心をする ('to make a resolution').