Understanding how much electricity a device uses is important, but usually unknown. Usually the closest we can get is to see a yellow sticker stating that is it energy efficient when we buy it. Beyond that, most people have no idea how much they pay for the use of their appliances. Somehow we need to find a way to see what energy is used when we hit the switch so we can decide whether or not we want to pay for the usage of it.
A simple way is to watch your electric meter. Turn off everything electric in your house. Then make a note of the electric meter's settings and turn the device back on. After a few minutes record the settings again. For instance, measure how long it takes to go one time around the dial and figure how much electricity you used during that time. You can calculate the cost of the device by the rate listed on your electric bill. Do this for each device you think may be using a lot of electricity. Some of the obvious energy hogs are dryers, electric stoves, hair dryers and air conditioners.
Buy a watt-hour-meter. This is a simple device that is rather inexpensive that simply plugs into the wall and you then plug the device into it. It will display how much electricity is being used on a digital screen. After a few simple calculations, you can figure out how much you are paying. This is good for devices that don't use a constant supply of electricity like refrigerators which cycle on and off.
Read the label. Most devices have a label somewhere that tells exactly what the maximum use is. Since most electric wiring in the US is for 110-120 volts, you can figure the usage by multiplying the number of amps by 120. For instance, if something says it uses 6 amps, that would mean it uses 6x120 or 720 watts per hour. Some devices have a transformer on them that converts the electricity from AC to DC and might read, "Input 9 V., .05A". That means you multiply the DC current which is 9 volts x .05 amps which is 4.5 volts. This is not a consistent way to measure the electricity used, since it is the maximum use and maybe your device only gets that high for 5 minutes on the hour. It is only a general measurement.
Get a whole house meter. This is a gadget that is installed by an electrician and it will let you know exactly how much you have used at any point in time. It costs around $150 and will take about 15 minutes to install. With this, you can gauge how much electricity you have used and how much more you want to use.