A roller brush is used to literally roll paint across a surface. It should be applied in an M shape before the rest of the space is filled in. A regular paint brush should be angled at 45 degrees in tight corners and along the edges to create a smooth paint surface.
A roller should leave an even and smooth coat of paint with no marks. A regular paint brush will leave brush strokes if used on large areas.
Natural rollers are made of lambswool or mohair, while natural brushes can be made of any animal hair. Either brush can also be made of nylon or polyester.
Load a roller brush from one end to the other and clean it thoroughly afterwards. With a regular paint brush don't dip the paint brush all the way to the handle. This will cause the paint to drip and fall off the brush.
Depending on where you are painting, you may need to use both types of brushes. A roller brush will be needed to cover the walls and ceiling of a room, while the regular paint brush will be used on door frames and floor moldings.