Splitting mains power into multiple relay-switched circuits
Option the first would be skip this if you are truly unfamiliar with mains power - it's not something you should attempt without having a very good idea what you are doing and how to do it right, especially if you are in a 220-240V mains region.

Use a box; One large enough to mount a normal wall-outlet type duplex receptacle in, and all your connections, SSRs and the RasPi and its power supply inside.

Use either a terminal strip (crimp-on spade connectors optional) or wire nuts to make the connections inside the box. If the box is plastic, done. If the box is metal, be sure to connect it to the grounding wire.