For the sake of simplicity, this is what you should know:
Fish, Olive Oil, Peanut Oil, Canola Oil, Fish Oils, Flaxseeds, Avocado, and Nuts (peanuts, almonds, walnuts, etc)
These are: Monounsaturated Fats (MFA's, best) known as Omega-3's (fish & nuts) and Omega-6's (nuts)
What they do: improve brain function and reduce blood pressure by increasing HDL (good cholesterol) and lowering LDL (bad cholesterol)
Vegetable oils such as corn oil, safflower oil, and sesame oil
These are: Polyunsaturated Fats (PUFA's), which are a bit different structurally that MFS's
What they do: decrease HDL (good cholesterol) and decrease LDL (bad cholesterol)
Most Americans get more than enough PUFA's, and an overabundance can be dangerous. We should be aware that overheating these oils can actually cause them to have unhealthy properties.
If we must (...and I must)
Animal fats, such as those in meats and dairy, and some tropical plant oils such as coconut, cocoa, and palm oil
These are: Saturated Fats, which are solid at room temperature
What they do: Increase HDL "bad" cholesterol and LDL "good" cholesterol
Try to: Choose lean meats, such as lean cuts of beef or chicken, and low-fat dairy products. Eat full fat as a treat!
Hydrogenated Oils, Partially Hydrogenated Oils, Vegetable Oils solid at room temperature - found in many peanut butters, butter spreads, and processed foods
These are: Trans Fats
What they do: This is a man-made product that decreases HDL "good" cholesterol and increases LDL "bad" cholesterol.
Try to: Read labels! If it says "Hydrogenated Oil" or "Partially Hydrogenated Oil" it has Trans Fats (even if it advertises Zero trans fat on the label). Limit these items as much as possible.