If you have an old 1151C1 power supply, you just go wall jack to power supply, power supply to phone (8-conductor cable here), and connect the sidecar to the MOD jack on the phone.

If you have a standard SPPoE power supply, they included a T-adapter (2 jacks with a pigtail). The pigtail goes into the wall jack, which needs to be 8-conductor, or use an 8-pin coupler to the standard line cord plugged into an RJ-11 jack on the wall. Then a CAT-5 cable from the PoE injector to the T-adapter, and another CAT-5 cable from the other side of the T-adapter to the phone.

[Linked Image from i.imgur.com]