For an easier usage, NEI and WAILA could be installed, which show the A and B sides on the Invert Cell.
The Invert Cell has two A and two B input/output sides, located opposite. It can connects to red alloy cables, redstone, an adjacent circuit, machine, lamp or anything that can be controlled with redstone signals.
Redstone signal are transmitted between the A-sides and B-sides, but if the the A-line is "off", then the gate switch "on" the B-line, even no signal receives one of the B-sides ("A = off" result in "B = on"). This function does NOT expire vice versa ("B = off" doesn't result in "A = on").
This function is a negative interaction. For a positive interaction between the lines ("A = on" result in "B = on"), you must use the Buffer Cell.
If the A-line is on, then the gate switch off the B-line, but a redstone signal/pulse can transmitted on the B-line.
Using the screwdriver from Project Red, the orientation of the gate can be changed freely in all four directions.