When you open the box to your Yealink, there should be two separate cables.
A power supply cable
An internet (Cat5) cable
You can connect the Yealink to the internet in several ways - directly to your router or into a wall socket.
Insert one end of the internet (Cat5) cable into the back of the Yealink in the Internet port and the other end into your router or wall socket.
On the back of the Yealink, insert one end of the power cable into the DC5V port and the other end needs to be connected to your mains power outlet.
After the Yealink is connected to the network and supplied with power, it automatically begins the initialization process. After startup, the phone is ready for use.