You will need to be close to your router or a network port to be able to install your power supply.
First of all plug a patch cable into phone port on your power supply, this will look something like the below
Plug the other end of that patch cable into the port in the back of your Mitel handset pictured below
Then we are going to need to plug another patch cable into the LAN/Network port of the power supply pictured below
Then plug the other end of that cable into your network source. This can be your router your switch or even a CAT 5 port that has a live network connection. Some samples of each are below