To put it [I]very[/I] simply...once the skin and underlying layers are cut, it fills with a blood clot. Then cells called fibroblasts move into the clot from surrounding tissue, breaking it down and replacing it with scar tissue. This scar tissue is composed of collagen and fibrogen, the same protein as normal skin. The difference is the protein fibers in normal skin have a random basketweave pattern, while those in scar tissue align in a single direction.
The larger (deeper) the wound, the longer it takes to heal, the more scar tissue. As your skin naturally replaces itself, the scar will eventually fade. Again, depending on the severity of the wound. Other factors include race, age, heredity.
There are many ways to remove scar tissue including chemical, laser, massage, etc. The idea behind all of this is to break up those aligned strands so new tissue can form. Using creams to keep the skin moist and pliable, ex foliating as you massage.
There are drugs that stimulate new tissue growth but these are reserved for deep, hard to heal wounds.
Sometimes, scar tissue can adhere to an underlying structure causing obstruction (as in abdominal) or difficulty moving (as in a joint).
When I went to PT after my first surgery, the therapist did deep massage to break up the scar tissue restricting joint movement. There's also ultrasound (deep pulsating sound waves) that help break up (relax) deep scar tissue.
WHEW! Hope that wasn't too boring. Tomorrow there will be a quiz