There are many ways to create sentences, but almost all sentences in the English language are made up of some basic elements. The basic unit on which most sentences are built is the Independent Clause. This is made up of a subject (something/someone) doing an action (verb).
Simple sentences are made up of one Independent Clause. To learn more, see How To Write Correct Sentences: Part 1-Simple Sentences.
These Independent Clauses can also be combined to form Compound Sentences. Compound sentences can be formed using Coordinating Conjunctions, Transitional Expressions and Conjunctive Adverbs, or semicolons. To learn more, see How To Write Correct Sentences: Part 2-Compound Sentences.
Another sentence type–the Complex Sentence–uses Subordinating Conjunctions to connect Independent Clauses. To read more about this, see How To Write Correct Sentences: Part 3-Complex Sentences.