What's the difference between a simple and compound sentence?

The difference between the both is that A simple sentence consists of only one clause. A compound sentence consists of two or more independent clauses

Clauses meaning: a unit of grammatical organization next below the sentence in rank and in traditional grammar said to consist of a subject and predicate.

Answer: A simple sentence consists of only one clause. A compound sentence consists of two or more independent clauses. A complex sentence has at least one independent clause plus at least one dependent clause.