Zero Conditional. When you talk about the facts or general truths, you use Present simple in both sentences. For example,

When a bee stings you, it dies. (Когда пчела жалит, она погибает.)

First Conditional. When you feel that something will really happen, you use if + Present simple . In the other part of the sentence ( not the if-part) you usewill +infinitive . For example,

My dog will feel better if it plays with other dogs. (Моя собака почувствует себя лучше, если будет играть с другими собаками.)

Second Conditional. When you imagine, wish or dream of something, you use if +Past Simple . In the other part of the sentence (not the if-part) you use would orwouldn't +infinitive .

For example,

I would keep a dog if I lived in a house. (Я бы держал собаку, если бы я жил в доме.)