How Does a Microbiome Work in Humans?

The bacteria in our gut have many important functions, but the one you're probably most familiar with is breaking down the food that we eat. We can't digest dietary fiber without our microbes. They ferment the fiber into important products for our health. There are certain vitamins that our bodies can't make. The microbes make it for us. So if you had to think about how this actually works in humans specifically, how does a microbiome work in humans?