Using a puff:
Powder puffs come in a myriad of sizes, shapes and colors, but the most important thing to consider is the nap of the puff. A medium nap (think chenille) is the best to apply powder. The fine-nap puffs that usually come with powder cause streaking. They may also actually remove foundation. If the nap is too long (such as marabou) you'll get fuzz on your face. To use: It's best to use a puff if you tend to shine excessively or when using a powder foundation. Do not apply too much powder at once. Better to blot oil later in the day than have a cakey, overdone look to your face.
Using a brush:
A brush allows you to apply a lighter amount of powder than a puff. Large and fluffy, powder brushes can be used with both loose and pressed powder formulations. To use: Dip the brush in the powder and tap it to shake off loose powder. Then brush the powder evenly over your face in downward strokes
You want to go in the direction your facial hair grows in order to get the most even application.