Mold is a fungus that can grow anywhere there is a source of moisture, a source of organic matter, and proper temperatures. As such, it is often found in most environments. The mold produces spores which are carried in the air and can be deposited on interior surfaces, and stay there dormant until sufficient moisture is available to cause the spores to grow.
The mold can grow quite quickly if deposited on organic matter and there is poor circulation. Areas of concern would be any wooden surface, carpets, and dry wall panels, which includes all wall cavities, flooring and ceilings. Once water has entered a building, all affected surfaces will soon become moldy and need to be cleaned or removed as necessary, and the area completely dried out before being put back into service.
You may be able to smell it once it starts to spread. It will usually appear black in color. You can discern between mold and just surface dirt or other discoloration by spray applying a bleach solution at about 1 part to 8 parts water. If it turns clear, it is mold.
The 1/8 bleach solution can be used to clean the surface by leaving it on the mold for 15 minutes, and then wipe it off using warm water and a clean towel until no signs of it remain. The mold may leave a stain on the affected area. Ventilate the area until completely dry, then vacuum the area well, and dispose of it in a sealed bag. If the affected area is large you may need to have mold remediation work done by a professional contractor. It is always wise to clean up any mold as soon as it is noticed, as many people can have allergies and respiratory problems from living in a moldy indoor environment.
It should be noted that using bleach or sanitizers will only clean up existing mold, and more mold can appear if the surface is exposed to moisture once again, so it’s important to correct the moisture entry problem. One long term solution is to coat the treated surface with an antimicrobial coating that inhibits mold growth.