To get down to brass tacks means to become serious about something. It refers to the fact that putting in brass tacks requires serious concentration as even a slight distraction means a serious injury to the fingers or hand.
1. The Professor warned his students that if they did not stop their constant cricket-watching and get down to brass tacks, they would surely fail in the term exam.
2. The doctor got down to brass tacks as soon as the diabetic patient entered his clinic.
3. The minute Mayank returned home from his friend's party, his father got down to brass tacks and told him it was time he lent a hand in the business instead of fooling around.