Compound
Sentence

Keith brushed his teeth, and he went to bed.

• The two clauses are separated by a comma and a coordinating conjunction (, and).
• The subject of the second clause is explicitly stated. ("He" is the subject of the second clause).

Hybrid
Sentence

Keith brushed his teeth and went to bed.

• There is no comma between the two clauses (or two predicates).
• The subject of the second clause is omitted (left out), because it is implied. (The reader understands that it is Keith who went to bed.