0 Conditional
General Truths / Facts
If this thing happens, that thing happens.
Simple Present + Simple Present
1st Conditional
A possible condition and its probable result
If this thing happens, that thing will happen.
Simple Present + Simple Future(will + V)
2nd Conditional
A hypothetical condition and its probable result
If this thing happened, that thing would happen.
If this thing is happened, that thing would be happening.
Simple past + Present conditional(would + V) OR Present continuous conditional(would be + V(ing))
If this thing happened, that thing would happen. (but I’m not sure this thing will happen) OR that thing would be happening.
3nd Conditional
An unreal past condition and its probable result in the past.
If this thing had happened, that thing would have happened.
If this thing had happened, that thing would have been happening.
Past perfect**(had + V(pp)) + **Perfect conditional(would have + V(pp)) OR Perfect continuous conditional(would have been + V(ing))
If this thing had happened, that thing would have happened. (but neither of those things really happened) OR that thing would have been happening.