Embedded ring is one of the 2 solution currently used in onshore wind farm foundations.
Basically is a steel cylinder with several holes: a set of hole all around it to allow radial steel reinforcement bars to cross it and another set of holes for the passage of Medium Voltage cables and the earth copper wire.
This element is lifted with a crane, and it is put on the foundation hole, above the blinding concrete.
Than the topographers levels it, and all around it the steel bars are positioned.
After, the concrete is poured and vibrated, and it is left for several days to let the concrete harden. The top of the embedded ring has several holes that match with the holes in the first segment of the tower: they will be bolted together when the tower is positioned