Beer bread is a quick bread, leavened with baking powder rather than yeast, in which beer stands in for most or all of the liquid in the dough.
The beer's carbonation adds a little lift and its residual sugars and hop character flavor the loaf, but the rise comes mainly from the baking powder; the yeast in a finished beer is largely inactive and doesn't leaven the bread the way fresh yeast would.
The basic recipe is flour, baking powder, salt, and beer, sometimes with added sugar or butter; it's mixed briefly and baked as a loaf, with no kneading or proofing required. Different beers change the flavor: hoppy IPAs add bitterness, stouts add malty sweetness. It's a popular, fast side for soups and stews in American home baking.