Modern English is a hybrid of many earlier languages, principally Latin, Greek and Anglo-Saxon. As such, it’s possible to communicate with a different level of formality depending on the choice of words used.
For instance, an object might be described as ‘round’ in everyday speech or as ‘circular’ in a technical description. You might describe a show as ‘funny’ to a friend, but as ‘humorous’ in an arts review.
Beginner writers often confuse the two tones, giving their characters long sentences, resulting in unnatural speech. In particular, I find that Victorian novelists were not good at writing an informal tone .
Additionally, the structure of a given sentence can support its tone. It’s a common misconception that a sentence can’t begin with a conjunction (and, but, &c) nor end with a preposition (with, from, &c). While these traits should be avoided in formal writing, you can begin and end a sentence with any words, provided they make sense in context.
An interesting blend of styles can be found in many Bible passages. While the language used tends to be formal in tone, the stories were often passed by word of mouth over several generations before being written. It’s therefore common to find verses that begin with conjunctions, much like someone would speak out loud.