Why is there a comma in an inverted scentence

[Unregistered]

Title says, no one in my class can figure it out grade 8 English. I'm thinking it has to do with clauses?

 

[Soup]

You're right. The comma separates the main clause from its subordinate clause. Here are two examples. (The subordinate clauses are underlined.)

[1] Had he understood the problem, he wouldn't have committed those mistakes.

[2] Should he decide to come, please telephone.

;-)