To utter some loud, forceful sound. I let out a shriek when the dog suddenly jumped on me. The lion let out an intimidating roar.

To make a low, guttural sound or speak in this manner. We slowly backed away as the dog growled at us. The old man growled at me to get out of his yard.

To speak so that one's voice has a low, guttural tone or quality. A noun or pronoun can be used between "growl" and "out." I bolted after the old man growled out a command to get out of his yard.