Once the spores are on the bread, they will need a source of nutrients. The bread provides the nutrients. The mold will also need a source of water. Again, the bread will provide the water, but you don't want to let the bread dry out too much. You will need to keep the bread in a closed container.
Zip lock bags work great.
If your bread is already kind of dried out, you might include another source of water. A damp paper towel can provide another source of moisture. Another important consideration is the source of bread. Some breads include preservatives. These preservatives will slow down the growth of bread.