This means that when you put words in a series, they need to match (or parallel) the grammatical structure.
Marlene ate chili, chicken, peas, and sliced her bananas. The last item, sliced her bananas, isn't parallel.
You can correct it this way: Marlene ate chili, chicken, peas, and bananas. Or you could write, Marlene ate chili, chicken, and peas. After that, she sliced her bananas.
When I write a series of words,
each word will match the grammatical structure.