Answer:
Syntax is what makes up sentence structure. Here are some examples of various forms of syntax.
-Simple: I went to the mall. (Simple because only an independent clause.)
-Compound: I ate a cake, and I played the flute afterwards. (Two independent clauses linked by a coordinating conjunction)
-Complex: It was a wonderful day until the bus ran me over. (independent clause and dependent clause)
These are the basics. Now let's get into some syntax and how it can reflect tone and mood.
I walked to the mall. I saw a man. He had a gun. It was a scary. (These are read very disjointedly because they are all simple sentences. However, it creates some anxiety because you read it quickly it seems. Also, the parallel sentence structures help to awaken the reader's senses.)
I walked to the mall and along the way I saw a man with a gun; suddenly I was fearful. (This one is much less boring, but it also doesn't give the same sense of anxiety because it is all joined. It seems like something is missing because it is only in one sentence. However, the semicolon helps to keep a sense of anxiety)
Depending on the situation, the author might use a different type of sentence structure, or syntax.