A great explanation from the Happy Herbivore:
Active yeast and nutritional yeast are completely different products that are used for two different things. When people ask me if they can swap out the two and use them interchangeably- I always have to tell them no because the results in whatever they’re making will come out completely different!
Active yeast works as a leavening agent in breads and other baked goods. It’s primarily used to make your baked goods rise and add fluff to a piece of bread or a cinnamon roll. Active yeast can come in a jar, or it can come in little envelopes found in the baking aisle of your grocery store.
Nutritional yeast is a deactivated yeast, so it won’t make things rise and is not a replacement for yeast when baking.
It has a cheesy, nutty flavor that you can use in sauces or as a topping, like sprinkled on popcorn. Nutritional yeast can be bought online or at most health food stores, and comes either as a powder or flakes. It is a complete protein, a good source of vitamins and is dairy & gluten free. Most brands are also fortified with B-12.
Here’s a video on nutritional yeast that might answer more of your questions: