Hi Lil Jo,
You should check out the science fair project guide on the science buddies website. This guide will help you plan your experiment. You also need to learn as much as possible about bread mold. Here is a website that includes lots of background information: http://www.madsci.org/FAQs/micro/molds.html
For your project, you will want to ask a question that can be answered with an experiment. In the experiment, you will keep all conditions the same, except one independent variable that you change. For example, if you want to find out how the ingredients in bread affect mold growth, you will want to have bread samples that are identical except one ingredient, like whole wheat or whole rye flour. The temperature, amount of light, and amount of moisture would be constant. If you use bread from the store, make sure your samples all contain the same preservative, or no preservative. Mold spores are always in the air, so if you put a piece of bread in the dark with the right amount of moisture and at the right temperature, it will always grow mold.
One problem that many bread mold science projects have is that results are not measured. It is always better to have an experiment with measurable results, so do plan this part of your experiment. You could measure the time it takes for the mold colonies to appear, measure the time until spores (the dark color of mold colonies), or measure the percent area of the bread that is covered by the mold. Perhaps you could think of something else.
Experiments with bread mold can make really great science fair projects, so I hope this will help you get started. Please do be careful and don't breathe the mold spores; always keep the moldy bread covered when you are working with it.