Had I known about the traffic, I would have left earlier. Had she studied harder, she would have passed the exam. Had they arrived on time, they would have seen the opening ceremony. Had we not missed the train, we would be there by now. Had you called me, I would have helped you. Had it not been for your support, I would have given up.
Were + subject (Second Conditional)
Were I you, I would apologise immediately. Were she my daughter, I would be very proud. Were he to ask for help, I would say yes. Were we to win the lottery, we would travel the world. Were they here, they would agree with us. Were it not for the rain, we would go outside.
Should + subject (First Conditional)
Should you need assistance, please contact our support team. Should she call, tell her I'll be back soon. Should he arrive late, start the meeting without him. Should they decide to join, we will need more chairs. Should the weather improve, we will go to the beach.
Mixed and Negative Examples
Had I not seen him, I would have worried. Weren't she so busy, she would help us. Had I studied medicine, I would be a doctor now (mixed). Were I not afraid of heights, I would have gone skydiving (mixed).