The Shield connects one of the Imp’s UARTs (Imp pins 5 and 7) to either the Arduino hardware UART or a software serial on pins 8 and 9. It defaults to the software serial, but there are jumpers on the bottom side to set it to the hardware serial. A couple imp pins (8 & 9) are also connected to LEDs. They can be disconnected via jumpers on the bottom, if you’d like.
Because the Electric Imp can draw up to 400mA on the 3.3V line, this shield has its own voltage regulator which is fed from the 5V Arduino line. Most Arduino compatible boards should be able to handle this amount of draw but beware that some clones that use less robust VREGs could see trouble.
Note: This shield does NOT come with the Electric Imp card.