the difference between unsaturated and saturated fats

While both unsaturated fat and saturated fat are in a variety of foods, studies have found that these fats are not created equally. Unsaturated fats can be beneficial to your heart, whereas saturated fats could be detrimental to your cholesterol and your heart.

Saturated fats
      * found in animal products and processed foods, such as meats, dairy products, chips, and pastries.
      *The chemical structure of a saturated fat is fully saturated with hydrogen atoms, and does not contain double bonds between carbon atoms.
      *Saturated fats are not heart healthy, since they are most known for raising your LDL cholesterol (“bad” cholesterol).

Unsaturated fats,
      * found foods such as nuts, avocados, and olives. They are liquid at room temperature
      *  their chemical structure contains double bonds.
      * unsaturated fats are also heart-healthy fats - they have the ability to lower LDL cholesterol and raise HDL cholesterol ("good" cholesterol).

So, if you are trying to follow a cholesterol-lowering diet, eating unsaturated fats should not raise your cholesterol levels further. However, you should try to avoid foods high in saturated fats, since consuming a diet high in this type of fat could increase your risk of having high cholesterol and heart disease over time.
_Sources:

Rolfes SR, Whitney E. Understanding Nutrition, 3rd ed 2005.