A sponge is a quick way to add an extra flavor profile to your bread. I use a sponge especially when I am pressed for time or need to make a loaf of bread and did not make a starter or preferment the night before. Sponges are easy to create even if your recipe does not have instructions or call for making one. Depending on who you talk to a sponge can be made different ways, but I think I have a pretty good rule of thumb that you can use to transform any straight dough method into one utilizing a preferment.
I usually will take take half of the flour that is called for in the recipe with all of the water and a small fraction of the yeast (usually 1/4-1/2 tsp). Stir these ingredients together in the bowl that you are going to make the finished dough in. The consistency should be like a thick pancake batter. Cover the bowl with plastic wrap and let it stand anywhere from 1 to 4 hours. If you only let the sponge rise for an hour then you will need to add the rest of the yeast the recipe calls for, but the longer you let the sponge ferment the less yeast you can put in the final dough. I will always try to cut back on commercial yeasts where I can, because they add a yeasty flavor profile instead of a clean nutty one that you can get naturally. Any form of preferment can aid in this. This extra step will give your dough a jump start on the fermentation process which will add extra flavor and shelf life to your finished loaf.