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These should be dead easy to set up!
The smaller one of the two needs to be plugged into a wall socket (not a powerstrip if at all possible), and then you plug in the larger of the two plugs with the WiFi ability remotely within the house. They will work if they are on separate ring mains but are better if on the same one.
When it comes to setting up the WiFi, use a separate SSID for the WiFi on the extender and manually connect clients to either the Router SSID or the extender SSID - you can't use the same SSID because that will not work with these! *And for best results leave the channel setting on "Auto"!