A voltmeter is connected in parallel with a device to measure its voltage, while an ammeter is connected in series with a device to measure its current.
Source: Boundless. “Voltmeters and Ammeters.” Boundless Physics. Boundless, 21 Jul. 2015. Retrieved 02 Sep. 2015 from https://www.boundless.com/physics/textbooks/boundless-physics-textbook/circuits-and-direct-currents-20/voltmeters-and-ammeters-153/voltmeters-and-ammeters-542-11287/