I've read in these forums that you should eat an increasing amount of Dietary Fats and not Saturated Fats when you are trying to build mass. What foods have dietary fats and what have saturated fats? I don't really know the difference between the two at all.
Dietary fats refers to ALL fats you eat. Saturated fat is one type of fat and should be limited. Generally, a saturated fat is solid at room temperature. Think fat from meat. Even after the meat is cooked, and the fat melts, but then solidifies again, it's saturated. Not good for health. Other types of fat are monounsaturated, polyunsaturated (both good fats), transfats aka partially hydrogenated vegetable oil (bad fat).
Any fat that goes in your mouth is a "dietary" fat, whether it's a fat all on its own (for instance, olive oil) or fat naturally present in food (for instance, the small percent of fat in your typical chicken breast).
I'm not quite sure what you mean, here, or where you read what you read. Essential fats, such as are found in fish oils, flax, hemp and various nut oils (you may have run into mention of them under their aliases of Omega 6 and Omega 3) should always be a part of the healthy diet. You should supplement with fish oil, and/or eat oily fish such as salmon, herring, and/or flaxseed, walnuts and other high-Omega nuts and seeds.
Or, possibly, you mean, "when trying to build mass, one should increase one's dietary fats, but not by eating more saturated fats." Saturated fats, in general, are those found in animal products. (The one exception is tropical oils like palm and coconut oil, which were once demonized. Research is now suggesting, however, that they don't act like animal saturated fats in the body, but may instead be beneficial in some ways.) Anyway -- butter? All saturated fat. Likewise full-fat dairy products, likewise fatty meats like bacon and ham. Saturated fat is not so good for your circulatory system (in other words, it may increase your chances of a heart attack, stroke, or other such incident) and may raise "bad" cholesterol.
In short, if that is what you mean, then if you are trying to build mass and one of the techniques you wish to use is to increase your dietary fat, then do not go crazy on the breakfast bacon; instead, increase your consumption of, for instance, nuts and nut butters and other higher-fat foods that don't contain a lot of saturated fat.
And, needless to say, don't go anywhere near trans-fats. These chemically-altered fats are of the Devil, and you can mostly spot them by the word "hydrogenated" or "partly hydrogenated" on a label. Don't be adding dollops of margarine to your bulking diet!
Yea what he said and to put it more basic. Keep your sat. fat as low as possible whether you are cutting or bulking. Its bad for you anyway you look at it, be it being a fatass or have clogged arteries.