Using this PetSafe Wireless Pet Containment System is easy. First, find a standard wall outlet close to the area where you want to keep your pet. Plug in the Transmitter. Put the Receiver Collar on your pet, making sure it fits properly around their neck (it fits necks from 15 to 71 cm). You can use the 50 Training Flags to mark the containment perimeter. When your pet gets close to the perimeter, they'll hear a warning tone. If they keep going, they'll get a mild electrical stimulation, but don't worry, it stops after 30 seconds. You can add more pets by getting additional Add - A - Dog® Wireless Receiver Collars (sold separately). Remember to replace the 1 x 6 Volt battery (which comes included) when it runs out. Keep the system away from water and store it in a dry place when not in use. Follow the Operating and Training Guide for more detailed training tips to help your pet get used to the system quickly.