The gravity feed is a top mount cup that uses gravity to pull the paint down into the airbrush. This feed is great for airbrush art designs that call for fine detail as the gravity feed uses less air pressure. The less air pressure means that you can use slower movements when airbrushing. The bottom feed is where the cup is mounted to the bottom of the airbrush and the paint is brought up via a siphon tube. In 1893 the world seen a more modernized version of airbrushing when Charles Burdick patent the first airbrush device. This device would be used for retouching photographs until around the 1920. During the 1930s airbrush increased when advertisement agencies jumped on the bandwagon to create advertisement of new products. Then go from there and start drawing out how you would have made it look. Once you are happy with it then airbrush it on to your project to create your own unique airbrush art design. If you don't want to get outdoors to look at new scenery and you don't want to go to the library then you can just surf the web. One way is all the design to fully dry then place a cloth over it and iron the shirt with the cloth between the t-shirt and the iron. Always keep the iron moving though so that you do not burn the material. Another great way if you are doing this at home is to allow the design to dry then turn the shirt inside out and throw it into the dryer for about 40 to 45 minutes on the highest heat setting. These paints are ready to use and will save you from having to deal with thinners and such. Save those types of paints for when you have gained yourself some experience with airbrush art. Stick to ready to use black paint from Golden Airbrush Colors because it really does not matter how the paint looks at this point. In a single action airbrush the trigger controls the air flow. In a dual action airbrush the trigger controls both the air flow and the paint flow. Beginners should really take the time to practice on how the trigger works so that they can perfect their ability to airbrush. Your airbrush will have a back lever as well that acts to shut off the air flow and paint flow when the trigger is released.