Voltmeters and ammeters are very self-explanatory. Voltmeters measure the voltage drop between two different points, while ammeters measure the current flowing through the wire at a specific point. Though the general idea is easy to master, there are more to these two objects. For ammeters, the resistance of the device overall is generally very low; it is also connected in series to the circuit. For voltmeters, however, the resistance of the device overall is generally pretty high; it is thus connected in parallel to the circuit. See figure 19-33 for more details on how to connect these two devices. Since this was tested in the AP exam, be sure to know how to draw and connect them to a circuit!
Note: Do not worry about the picture at the right of the equal sign for each picture, but for those who want to know, (G) is a galvanometer, which moves the needle that measures the voltage or current.