Without getting into detail, this disease is basically having too many lipids or fat in the blood. Our body needs a certain amount of lipids to function. However, either due to genetics, diet or diseases such as diabetes the amount of fat or lipids in your blood is too high.
When there is an increase of lipids in the blood, it deposits in the arteries causing a disease called atherosclerosis or plaque build up. The rate that this builds up depends on the number of risk factors you have. These risk factors include diabetes, tobacco use, hypertension, aging and genetics. Good cholesterol or HDL may diminish the amount of plaque build up protecting you from having a heart attack. A heart attack occurs when the plaque that is building up becomes unstable and "ruptures". That is why you can feel good running and then have a heart attack long into your run.
A majority of high cholesterol is due to eating poorly over many years. A good diet can bring down your cholesterol. However, genes that cause your liver to make cholesterol may keep it high.
Hence, the basis for treatment, is a healthy low fat (low sugar) diet. Most people may need cholesterol medication to bring it down if the liver is making too much due to genetics. Exercise and weight loss will also aid in bringing down the LDL or bad cholesterol and can increase the HDL.
You should know your cholesterol and know your risk factors. One way to detect plaque in the heart is to have a CT scan of the heart looking for calcification which deposits in the plaque as it advances in growth.