before he/she willIntroduces an action that happens before another action involving เขา, which commonly means “he” or “she” and can sometimes mean “they.” จะ marks a future or intended action; in natural English, translate the phrase as “before he/she …” rather than “before he/she will …”.
TH: ก่อนที่เขาจะกลับบ้าน เราต้องทำงานให้เสร็จ
EN: Before he goes home, we have to finish the work.