Hyperlipidemia is a common problem. Unfortunately, over time this can be a serious condition that requires attention. I encourage you to talk to your primary care doctor
who can better explain, evaluate and treat this situation.
Hyperlipidemia means there is an elevated level of lipids (or fats) in your blood. Cholesterol is one type of fat. It is probably the most important type.
As for what causes it, there are really two major causes. One is diet. Cholesterol and fats come from animal products. Meats, cheeses, milk, etc are prominently involved. For example, eating fried foods and lots of red meat can raise your cholesterol. The second major cause is genetics. Your family may or may not be predisposed to high cholesterol. These variations depend on how your body processes the cholesterol. Other diseases can also worsen cholesterol, such as thyroid problems or diabetes.
Regardless of cause, it is important to treat. The major number to look at is the LDL Cholesterol or low density lipoprotein cholesterol. This is the "bad" cholesterol. For otherwise healthy people this should be less than 160 mg/dl.
To fix this, diet control (see above) and exercise is important. Losing weight and eating healthy are very important. If this remains elevated medications are available.
Talk to your doctor. If left untreated you will be at higher risk for heart attacks, strokes and leg problems.