means that something 'ought to be done', implying a certain moral obligation, or that it is the only reasonable course of action.
そういうことは本人に言うべきだ。 You ought to say things like that to the person themselves.
大変申し訳ございません。こちらがもっと早く気付くべきでした。 We are very sorry. we should have noticed this earlier.
先生は尊敬するべき人だ。 Sensei is a person you ought to have respect for.
Adjectives
Adding べき to an adjective requires it to be added with ある+べき+だ.
形容動詞
形容動詞＋ an extra で must be added.
教師はどの生徒に対しても平等であるべきです。 Teachers ought to treat all students equally.
元気であるべきです It ought to be healthy.
形容詞
requires a形容詞〜 to the く form.
親は子どもに対してもっと厳しくあるべきです。 Parents ought to be strict to their children.
する
When used with する, becomes すべき, or in full.
君のすべき任務は...
君のするべき任務は... As for the mission you ought to do..