Read the following sentence:
John went to the station and boarded the train.
This sentence has two parts: John went to the station and John boarded the train.
These two parts are joined by the coordinating conjunction and. Each one of these two parts has its own subject and predicate and therefore each one is a clause. Moreover, these are clauses of equal rank or importance and are independent of each other. Clauses of this kind are called coordinate clauses.
Now read the following sentence:
You can go by bus or by train.
This sentence too has two parts or two clauses: You can go by bus and You can go by train. These two parts or clauses are connected by the coordinating conjunction or.
Now consider this sentence:
He went to Mumbai, got his visa and came back.
This sentence has three independent clauses of equal rank – He went to Mumbai, He got his visa and He came back – and these are joined together by the coordinating conjunction and.
A sentence which consists of two or more co-ordinate clauses is called a compound sentence.