A potato ricer is a tool ( I got this one at target) that makes the potatoes lighter and fluffier. As I learned from Chef Kent Anderson, using a rice prevents over working the gluten in the potatoes which makes the potatoes heavy and starchy. After your potatoes are tender enough to easily poke with a fork, drain the potatoes and press the potatoes through the ricer. Put you butter and sour cream in the pot first (on low) and let them heat up as you rice in you potatoes.
Tips on good potatoes:
Don't over cook the potatoes, that makes them grainy
Do use, butter, sour cream, cream, or buttermilk (did I say or, I meant all!)Do use plenty of salt in the water