Working out always makes me hungry. Playing is all the cat does. Dad scolded Miriam for skipping her chores. No one likes my cooking.
A gerund is when a verb ending in -ing is used as a noun. In the first two sentences Working out and Playing are both used as the subject of the sentence. This makes them nouns. "Skipping" and "cooking" are also used as nouns in the sentences.
Dad scolded Miriam for skipping her chores.<span>No one likes my cooking. </span>Working out always makes me hungry.<span>Playing is all the cat does. </span>
It doesn't contain any punctuation, first of all, and second, it doesn't have a subject. To be a sentence, it must contain a subject. It also must contain one main clause.