1. THIRD
1.1. We can use the Third Conditional to talk about 'impossible' conditions, impossible because they are in the past and we cannot change what has happened.
1.2. FORM
1.2.1. if + past perfect, ...would + have + past participle
1.3. EXAMPLES
1.3.1. If we had bought that house, we would have had to rebuild the kitchen.
1.3.2. If I had worked harder at school, I would have got better grades.
2. FIRST
2.1. It's used to talk about things which might happen in the future.
2.2. FORM
2.2.1. if + present simple, ... will + infinitive
2.3. EXAMPLES
2.3.1. If I win the lottery, I will buy a car.
2.3.2. If they tell us they want it, we'll have to give it to them.
3. SECOND
3.1. The Second Conditional is used to talk about 'impossible' situations.
3.2. FORM
3.2.1. if + Past , Would + Infinitive
3.3. EXAMPLES
3.3.1. If I won the lottery, I would buy a car.
3.3.2. If we were in London today, we would be able to go to the concert in Hyde Park
4. ZERO
4.1. The ZERO conditional is used to make statements about the real world, and often refers to general truths, such as scientific facts.
4.1.1. The zero conditional is also often used to give instructions, using the imperative in the main clause.
4.2. FORM
4.2.1. IF + PRESENT SIMPLE + PRESENT SIMPLE
4.3. EXAMPLES
4.3.1. -If public transport is efficient, people stop using their cars.
4.3.2. -Meet me here if we get separated.