 Complex sentences are not complex. There are two types of sentences in IELTS writing. A simple sentence and a complex sentence. Here are two simple sentences. Put them together and you make a complex sentence. A simple sentence simply has one idea or one clause. A complex sentence has more than one idea and more than one clause. Many students believe that complex sentences have complex grammar structures in them like conditional and future structures. But this simply isn't true. To get a high score, use a mixture of simple and complex sentences. Remember complex sentences aren't complex and focus on accuracy.