Zero Conditional

• probability: 100% (exactly will happen)
• time: any time
• modals: when, if
• If + [condition: present simple] + [result: present simple]
• [result: present simple] + if + [condition: present simple]
• example: If you heat ice, it melts

First Conditional

• probability: 50% (there is a real possibility that this condition will happen)
• time: future
• modals: will, shall, can, or may
• If + [condition: present simple] + [result: WILL + base verb]
• [result: WILL + base verb] + if + [condition: present simple]
• example: If it rains, I will stay at home

Second Conditional

• probability: 10% (there is an unreal possibility that the condition will happen)
• time: future
• modals: would, should, could or might
• If + [condition: past simple] + [result: WOULD + base verb]
• [result: WOULD + base verb] + if + [condition: past simple]
• example: If I won the lottery, I would buy a car

Third Conditional

• probability: 0% (no possibility because it’s already happened in the past)
• time: past
• modals: would have, should have, could have, might have
• If + [condition: past perfect] + [result: WOULD HAVE + past participle]
• [result: WOULD HAVE + past participle] + if + [condition: past simple]
• example: If I had won the lottery, I would have bought a car

reference : english conditionals