An independent clause is a group of words that has a subject and a predicate. An independent clause does not depend upon anything else for its meaning. It expresses a complete thought. An independent clause is a simple sentence when it stands alone.
The officer blew his whistle and the car stopped.
In this sentence, there are two independent clauses. The first independent clause is The officer blew his whistle. The second independent clause is the cars stopped. These clauses could be written as two simple sentences by omitting the conjunction and. The conjunction and does not belong to either of the independent clauses. It simply brings the two independent clauses together in one sentence.
The officer blew his whistle. The cars stopped.