Electricity is measured in voltage, amperage, and wattage, so each home appliance you get will indicate those three electrical requirements. Your home air conditioner will be designed to work on either a standard 120 volt circuit, or, if it's a high powered unit, it may take 240V, which would require a special circuit in your house. Each 120V circuit in your house is rated for between 15 and 20 amperes and the 240V circuits are rated for 30A. If you draw more amps than the circuit is rated for, it will trip the circuit breaker.
The difference in electrical potential between two points is know as the voltage. Think of the electricity as water flowing through a pipe. A water tower has a lot of potential to spit out water and the empty swimming pool has a lot of potential to receive water. Connecting the two with a pipe results in a flow of water. The pressure of that flow is like the voltage in electricity. Higher voltage systems can move more electricity more quickly over the connection.
Amperes measure the amount of electricity that flows from one place to another over a given amount of time. Think of amps as the number of gallons per second flowing from the water tower into the swimming pool. A small hose will allow only a few gallons per second, while a big hose will increase the flow rate as long as there is enough water pressure. Appliances are said to "draw amps," referring to the amount of electrical current required to run them. It's similar to saying your toilet takes 1.5 gallons to flush. If you try to draw too many amps for a circuit, you will overload it and your circuit breaker will trip. Remove an appliance from that circuit.
Electrical power is measured in watts. When your electric bill comes in the mail it tells you how many watts you've used over the course of your billing cycle. The electric company measures the number of watts you use by looking at the amount of power consumed by all the electrical appliances plugged into your system. Think about flowing water again; if you had a fountain that recirculated the water, you wouldn't pay much for your water bill to run the fountain, but if you flush the toilet 100 times a day, your water bill will go up significantly. Amps are the flow of electricity, whether or not it does any work. Watts are the electrical energy that is used to do work.
A small AC unit will draw about 7.5A on a 120V circuit. So it can be used on the same circuit with small devices. A medium sized unit will draw closer to 15A on a 120V circuit, so it will need its own circuit free from any other devices. Large AC units can draw up to 30A and need a dedicated 240V circuit wired for them. Find the amps and volts used by your AC unit on the unit's metal label. On the top of the label is the manufacturer's name and the serial number. Underneath is a voltage requirement. Note: 120V circuits support voltages in the range from 110 to 120. Look for an amperage rating that will be somewhere between 7.5A and 30A. Don't choose an AC that requires more amps than your circuit can provide. Contact an electrician if you don't know the number of amps available on a circuit in your home.