A complex sentence is formed when you join a main clause and a subordinate clause with a connective.
Compound sentence
A compound sentence is formed when you join twomain clauses with a connective.
Main clause
A main clause is a clause that contains a subject,verb and an object. Main clauses makesense on their own.
Simple sentence
A simple sentence has one clause. It only has a verb and a subject.
Subordinate clause
A subordinate clause is one that relies on a main clause to make sense - it contains a subject and a verb, and adds extra information to the sentence. It needs to be attached to a main clause because it cannotmakesense on its own.