ON THIS WIKI
The MFSU, also known as MFS Unit or Multi-Functional Storage Unit, is a device for storing IndustrialCraft2 EU energy. The MFSU can store up to 10,000,000 EU (up to 512 EU/t input) and outputs up to 512 EU/t. The face with the dot is the output and the other five faces are inputs. You can change the facing of the dot by clicking on the block with an IndustrialCraft wrench. To pick up the MFSU with an IndustrialCraft Wrench, click on the dot.
The MFSU has a range of options for toggling a redstone signal upon conditions such as energy full or empty etc., allowing for example generation to be turned off automatically when the storage is full. Modes are cycled by clicking the redstone button in the GUI.
Here is a video for intermediate and advanced players that explains some of the more advanced concepts of IndustrialCraft power.