Simple Sentences

(independent clauses – each sentence stands on its own)

The apple fell from the tree.

The big, beautiful bird sang a lovely song.

Compound Sentences

(two sentences combined with a comma and a conjunction) 

The big, beautiful bird sang a lovely song, and the apple fell from the tree.

The apple fell from the tree, but the big and beautiful bird sang a lovely song.

Complex Sentences

(one sentence combined with a dependent clause, which could not stand on its own)

The beautiful bird sang a lovely song since the apple fell from the tree.

Since the apple fell from the tree, the beautiful bird sang a lovely song.