Do you want to learn about conditional sentences? Well, if you read this post, you’ll learn everything you need to know about the basics.
In English, we have four main types of conditionals: the zero conditional, the first conditional, the second conditional, and the third conditional. There are also mixed conditionals, but we can talk about those in another post.
In this post, I will first introduce the basic structure for conditional sentences. Then, I will give examples of the four main types of conditionals, explain why we use them, and show you the grammar you need to use for each one.  
Basic Structure of Conditional Sentences
Conditional sentences have two parts: the if-clause and the main clause (sometimes called the result clause). Remember, a clause is a group of words with a subject and a verb.
If the teacher is sick, we won’t go to class.
          [if-clause]                 [main clause]
The if-clause can come before the main clause, or it can come after it. When it comes after the main clause, you do not need a comma.
Zero Conditional
If it rains, the roads get wet.
We use the zero conditional to talk about things that are always true. It is often used for scientific facts. In the above example, the roads always get wet when it rains.
If-clause: use a present simple verb
Main clause: use a present simple verb
First Conditional
If it rains, we will go home early.
The first conditional talks about future conditions and results. So? In the above example, will we go home early? We don’t know. We will have to wait to see what the weather is like.
If-clause: use a present simple verb
Main clause: use will + infinitive verb
Second Conditional
If I owned a restaurant, I would eat there every day.
We use the second conditional to talk about present unreal (imaginary) situations. In the example, I do not own a restaurant.
If-clause: use a past simple verb*
Main clause: use would/could + infinitive verb
*Yes! It’s true. We are talking about a PRESENT unreal situation, but we use the PAST simple. I know it’s weird, but trust me — it’s correct. 
Third Conditional
If I had gone to the party, I would have brought a gift.
The third conditional talks about past situations that did not happen. In this example, I did not go to the party. 
If-clause: use the past perfect (had + past participle verb)
Main clause: use would/could + have + past participle verb