Do not get confused; A sentence type refers to 'interrogative, declarative, exclamative and imperative' sentences, while a 'Sentence Structure' refers to the syntax of sentences (eg, Simple Sentences, Complex, Compound, Compound-Complex) Apparently, this is one of the most common mistakes made in the English Language 3/4 exams :\
A simple sentence is a sentence that consists of one independent clause and can stand on its own
Eg- "He went to Church". An independent clause consists of a subject, a verb and an object, where the subject 'does' the verb, to (or in relation) to the object
A compound sentence is a sentence that consists of two independent clauses, linked by a co-ordinating conjunction
Co-ordinating conjunctions can be remembered by the acronym: F.A.N.B.O.Y.S (For, And, Nor/Neither, But, Or, Yet, So) All these conjunctions are used to link independent clauses together, and if you spot one in a sentence, chances are that sentence is a compound sentence (or compound-complex)
Eg- "I went to church and attended the seminar". (This sentence still consists of two independent clauses, since the second clause: "Attended the Seminar" can be re-written as "I attended the seminar" but the 'I' is ellipted as it can be inferred from the context of going to church in the first place).
Complex sentences are sentences containing an independent clause linked by a sub-ordinating conjunction to a dependent clause. A dependent clause (as the name suggests), cannot stand on its own, and needs to be introduced by an Independent clause, so inference from context can be drawn
Sentences such as "playing with it" is incomplete and cannot stand on its own, and hence is a dependent clause. When you link one of these with an independent clause, you have a complex sentence
A sub-ordinating conjunction is a conjunction other than the co-ordinating conjunctions (so, "Other than", "while", "after" could all be sub-ordinating conjunctions)
Eg- "I went to church while singing the hymn".
Compound Complex sentences are sentences that consist of two or more independent clauses (linked by a co-ordinating conjunction) and a dependent clause (linked by a subordinating conjunction)
Eg- "I was going to church and was driving at 85KM/PH while flooring the accelerator".
Independent clauses are: "I was going to church" and "I was driving at 85KM/PH" (yet again, the 'I' of the second independent clause is ellipted) and the dependent clause is "flooring the accelerator").