• Low-density lipoproteins (LDL) -Bad Lousy / Bad Cholesterol
  Contributes to plaque, a thick, hard deposit that can clog arteries and make them less flexible. This condition is known as atherosclerosis.
• High-density lipoproteins (HDL) - Good
  Experts believe HDL acts as a scavenger, carrying LDL cholesterol away from the arteries and back to the liver, where it is broken down and passed from the body.
• Triglycerides
  Triglycerides are another type of fat, and theyÕre used to store excess energy from your diet. High levels of triglycerides in the blood are associated with atherosclerosis. Elevated triglycerides can be caused by overweight and obesity, physical inactivity, cigarette smoking, excess alcohol consumption and a diet very high in carbohydrates (more than 60 percent of total calories).
• VLDL: (very low-density lipoprotein) contains very little protein. The main purpose of VLDL is to distribute the triglyceride produced by your liver. A high VLDL cholesterol level can cause the buildup of cholesterol in your arteries and increases your risk of heart disease and stroke.

Cholesterol level guidelines:
Reference Range (RWJ):
Total <200
LDL 65-129
HDL 40-60
Chol HDL Ratio ≤ 4.5

Good - Tot<200 LDL<100 HDL>60 tot/HDL<4 LDL/HDL <3.6
Bad Total>239 LDL>159 HDL<40 Trigly>199
Total cholesterol = LDL cholesterol + HDL cholesterol + (triglycerides/5).
Source: What Your Cholesterol Levels Mean | American Heart Association
My friends doctor says there are other formulas for total cholesterol.

The primary predictor for Coronary Artery Disease (CAD) (Atherosclerosis) is a ratio.
It was Total/HDL, now it is LDL(bad) / HDL (good).

LDL/HDL Ratio:  Men      Women
1/2 Avg. Risk   1.0-2.3   1.5
      Average   2.4-3.5   3.2
     Moderate   3.5-7.1   5.0
3X average risk ≥ 7.2  6.1
I couldn't find any consistend guidelines for LDL/HDL ratio.
The above numbers are averages from a couple of sources.

In the summer of 2004 by the National Heart, Lung, and Blood Institute (NHLBI) that high-risk patients start recieving medication when their LDL levels hit 70.
See: Announcement by the >
The National Cholesterol Education ProgramÕs (NCEP) defines high-risk patients as those who have coronary heart disease or disease of the blood vessels to the brain or extremities, or diabetes, or multiple (2 or more) risk factors (e.g., smoking, hypertension) that give them a greater than 20 percent chance of having a heart attack within 10 years.

Drugs:
Statins are the worldÕs leading cholesterol-lowering drugs. Statins work by inhibiting an enzyme called HMG-CoA reductase that controls production of cholesterol in the liver.

While best known for their ability to lower serum cholesterol, statins also reduce artery-damaging inflammation that can result in a life-threatening blood clot.
By lowering cholesterol, statins also appear to stabilize plaque, artery deposits that can break loose and cause a heart attack or stroke. And they may cleanse arteries of plaque that has not yet become calcified.

More than a quarter of Americans older than 40 are taking a statin, a number that could rise to 46 percent of people aged 40 to 75 under the newest prescription guidelines (2015).

New guidelines (2015), put forth by the American College of Cardiology and American Heart Association, focus on four main groups who could be helped by statins.

• People who have cardiovascular disease, including those who have had a heart attack, stroke, peripheral artery disease, transient ischemic attack or surgery to open or replace coronary arteries.
• People with very high levels of LDL cholesterol, 190 milligrams or above.
• People with an LDL level from 70 to 189 milligrams who also have diabetes, a serious cardiovascular risk.
• People with an LDL level above 100 who, based on other risks like smoking, being overweight or high blood pressure, face a 7.5 percent or higher risk of having a heart attack within 10 years.

Side effects or ineffectiveness:
About 5 percent of people have distressing muscle aches, and some experience an unhealthy rise in blood sugar. Furthermore, Dr. Stephen L. Kopecky, a preventive cardiologist at the Mayo Clinic in Rochester, Minn., said that about 15 - 20% of people were ÒhyporespondersÓ Ð their LDL level is only minimally reduced or actually goes up on a statin. Source: For Statins, Cholesterol Care May Be Just the Start - The New York Times

Guideline-Based Statin Eligibility, Coronary Artery Calcification, and Cardiovascular Events; American Heart Association, 2015

Links:
Coronary Artery Disease
Stents