Good writers sometimes combine sentences to make their writing more interesting. That means they put sentences together! Two short sentences might have the same subject. The writer writes the subject once and then combines the two predicates in the same sentence.
The gorillas are eating. The gorillas are playing.
The gorillas are eating and playing.
Marcy likes to eat crackers. Marcy likes to eat cheese.
Marcy likes to eat crackers and cheese.
The children like to run. The children like to skip.
The children like to run and skip.