It shows itself in the form of decaying matter on a otherwise healthy plant. It creates a softening of tissue and plants will fall over and die. Root rot is the same as stem rot only affecting roots below soil level. Plants tend to just fall over and die for no noticeable reason. Fruit rot causes fruits to turn brown either soft or hard depending on the crop affected.
Wood rot is caused by extensive exposure to moisture.
Home owners generally know what this looks like when it affects processed wood. However, sometimes it's difficult to determine if a live plant has rot. Look for mushrooms growing on the tree. That's an indicator of excessive moisture in that area. Watch for softening areas that may turn brown or black.