When you've got a large surface area to paint then using a brush can be tedious, to get the job done quickly and still get a fine finish a paint roller is the obvious choice. Paint rollers come in a variety of sizes and types, the standard medium pile nine inch painting roller is fine for painting emulsion paints on interior walls and ceilings.
The smaller paint rollers and great for painting around hard to reach areas or on narrow surfaces. The Harris TaskMaster kit includes both pile paint roller sleeves and foam roller sleeves. Foam sleeves are best for clear finishes on wood because they tend to create the fewest bubbles.