Sentence Types by Structure
Beyond their function, sentences can be categorized by their structure or complexity. Simple sentences contain just one main clause expressing a complete thought (The baby has been born).
Compound sentences join two main clauses with a coordinating conjunction (I will chat you or give you a call). When you need to show that one idea depends on another, use complex sentences with one main clause and at least one subordinate clause (We bought the book which the teacher recommended).
The most sophisticated type, compound-complex sentences, combines multiple main clauses with one or more subordinate clauses (May called in the morning, she told us that she passed the exams, and her scores were very high).
Remember: You don't always need complex sentences to write well! Mix different sentence structures to make your writing interesting and keep your reader engaged.