If you have one of Intellijel's 7U cases, the µMIDI 1U can connect directly to the jacks on the back of the case. Therefore, you would not need the µMIDI Jacks 1U unless you had already connected the case jacks to another µMIDI 1U.
If you have one of Intellijel's 4U cases, you would need both the µMIDI 1U and the µMIDI Jacks 1U because the case does not have its own connections.
On the back of the µMIDI 1U there are two connection ports. The left one labelled POWER should connect to your case's power supply via a ribbon cable, making sure that the red stripe is aligned with the white line side marked -12V.
The MIDI-USB connection port will connect either to the corresponding port on the 7U case, or on the µMIDI Jacks 1U. Just make sure that the red stripe on the ribbon cable lines up with the white triangle on the PCB of the µMIDI. Then on the case jacks, the red stripe should match up with the White Line next to the header.