Note: The “if clause” does not always need to come first. The “if clause” can come second.
However, when the “if clause” comes first, it is followed by a comma.

Examples:

If I trip, I fall on my face.
But,
I fall on my face if I trip.

When I trip, I fall on my face.
Or,
I fall on my face when I trip.

Whenever I trip, I fall on my face.
Or,
I fall on my face whenever I trip.

DEFINITION: ZERO CONDITIONAL

The zero conditional is used to talk about something that is generally or always true. It can be used to express facts, rules, scientific laws, routines, and instructions.
The Zero conditional says that if (a) is true, then (b) is also true.
“If” or “when” can usually be substituted with “whenever.”

Formation: If clause = present simple, result clause = present simple

Example: If we drink too much, we are sick/hungover the next day.

DEFINITION: FIRST CONDITIONAL
The first conditional is used to talk about consequences for real world events. The first conditional is used when things are probable and likely to happen.

The first conditional can only refer to future events – things that have not happened at the time of speaking.

We use the first conditional to make a plan and a plan B or back up plan in case things go wrong.

Unless can be used instead of “if.”

Formation: If clause = present simple, result clause = “will” clause

Examples:

If we drink the whole bottle of vodka, we will be sick/hungover tomorrow.
We will be sick tomorrow if we drink the whole bottle of vodka.

Unless he hurries up, we will be late.
If he doesn’t hurry up, we will be late.

DEFINITION: SECOND CONDITIONAL

The second conditional is used to talk about things that are unlikely, improbable, or unrealistic. The ‘if’ clause describes the future event and the result clause explains the hypothetical consequences of the action.

Formation: If clause = past simple, result clause = “would” clause (conditional) + verb

Example: If I became class representative, I would get better coffee machines.

**Please notice that there is an important exception in English.
We can say, “If I were” in hypothetical situations expressed by the second conditional. Of course, you learned the correct form as “I was” or “If I was.” However, when the situation is very unlikely to come true we use the hypothetical “were” and it doesn’t matter if the subject is “I,” “you,” “he,” “she,” “it,” “we,” or “they.”

If I were a millionaire, I would buy a villa in Tuscany.
If she were a millionaire, she would buy a Ferrari.

DEFINITION: THIRD CONDITIONAL

The third conditional is used to talk about things that are impossible, usually because it is too late. The third conditional is used to say what would have happened if events in the past were different.

It is often used to express regret about actions in the past that the speaker would like to change.

Formation: If clause = past perfect (had + past participle), result clause “would have” clause (past conditional)

Example:
If I had known it was your birthday, I would have baked you a cake.
If I had heard the hot gossip, I would have called you.