Hi guys, can anyone tell me what a bread crock is used for?

I think - if it is like a bowl with a fitted lid - then it is something where you put raw sourdough bread mix. Sourdough is not made a batch at a time. You start off with a yeast dough and only use part of it. Leave the rest in the bread crock. When you make some more bread, you use a glob from the "starter" dough instead of fresh yeast for rising. You then replace some flour and water in the starter and it "ferments" or whatever yeast does so you can use more next time. It was used in pioneer days because the farm wives could not go to town to get fresh yeast. When yeast gets old, the bread will not rise. This sourdough starter mix can last forever if you do it right, and very seldom have to re-do it with fresh yeast.