Nespresso machines are automatic espresso machines made by Nespresso. They brew espresso of various sizes simply at the push of a button. The machines run on specially packaged "pods" or "capsules" that contain the coffee perfectly ground to work with the machines. The pods of course come in many "flavors" and types of beans and roasting darknesses.
The pods also come in consumer style and professional style. The consumer version is shaped and sized like a thimble whereas the pro version is shaped more like a UFO in the size of a Snapple cap. Consumer pods are meant for consumer machines and Pro pods are meant for the Pro line of machines. The two cannot be used interchangeably.
Nespresso recommends using filtered or distilled water. Experience says this is good advice as long usage with tap water can eventually develop deposits and scaling on the machine. Continued usage as such may render the machine inoperable or at the least in need of service.