Conditional sentences look at the result of a hypothetical situation. They consist of two clauses: the condition (or if-clause) and the consequence (or result).

Condition: If you do that again,

Consequence: I will go home.

They normally use the word 'if'. However, in more formal English, the subject and a modal auxiliary verb may be reversed to form the conditional. For example, Should you see her, say hello. See Unit 7 for more details. 

» TEFL Glossary