Both involve cooking proteins or veggies inside of some sort of cooking liquid. A stew involves covering whatever you're cooking completely inside of a cooking liquid, whereas the food you're braising is not completely covered in cooking liquid.

They are very similar, and outside of experienced cooks and chefs, not many English speakers probably know the difference. I believe a braise is when the food you are cooking is only partially submerged in the cooking liquid. If the food is fully submerged, it is a stew. Hope this helps!