How to write effective sentences? What is sentences? Types and importance of sentences

What is a sentence? 
A sentence is a group of words, almost always containing at least one subject and one verb, which expresses a complete thought or idea. Sentences always start with a capital letter, and always end with a full stop, a question mark or, in more informal writing, an exclamation mark.

Why are sentences important? 
In more formal written English clear structure is of paramount importance, and sentences are the foundation to achieving this. Unlike in spoken English, where the listener's understanding is greatly aided by intonation, facial expressions and body language, and where repetition, vagueness and uncompleted ideas are perfectly acceptable, in order to express yourself in formal written English you must write in clear, concise, complete, well - punctuated sentences.

Common errors while writing a sentence 

Sentences are incompleteSentences are incorrectly punctuatedSentences are too longSentences are too shortUsing run - on/comma - spliced sentencesUsing sentence fragments

Types of SentenceSimple sentencesCompound sentencesComplex sentences