You don't always need a powder. Face powders are primarily used to minimize shininess or excessively oily areas of the skin. Apply to the T-zone first (forehead and nose), then blend outward to other areas of the face with a brush or a puff.
There are two types of powders: loose and pressed. Loose powder has the consistency of confectioner's sugar. It is often packaged with a sifter, which further aerates the formulations. Light and airy, this form of powder is preferred by professional makeup artists because it's least likely to streak on the skin and it makes the most matte face. It also lasts longer than pressed powders. Pressed powder is treated under great pressure to create a compact, cake form. Oils are often added to the formula to ensure the powder sticks together longer, but they can make the powder more likely to streak.