Independent clauses, or simple sentences, always contain a noun (subject) and predicate, which tells something about the noun and must contain a verb. In addition, independent clauses can stand on their own, meaning they are complete sentences.
Coordinating conjunctions connects words, phrases or clauses together that have similar structure or content. The most common ones include for, and, nor, but, or, yet or so. Remember the word FANBOYS to remember them if it helps, as the first letter of each conjunction spells the word.
When two independent clauses, or complete sentences, are related, grammatically equal or similar, they are often connected with a coordinating conjunction Most of the time, the sentences are important and connected by either structure or content. Without the comma preceding the coordinating conjunction, the sentence is a run-on one. Consider the following examples:
INCORRECT: The dinner was short but the reception lasted well into the night.
Both the clause preceding and following the coordinating conjunction are independent clauses in the above example, so omitting the comma creates a run-on sentence.
CORRECT: The reception lasted late into the night, but the dinner before it was relatively short.
In the example above, both what precedes and follows the coordinating conjunction are independent clauses, so the comma makes the sentence grammatically correct.