The Low Voltage Transformer is mainly used to limit energy flow to 32 EU/t.
Unlike Real Life™, there is no actual "voltage" in IC². EU travels in "packets" through wires with near-infinite speed and has smart pathfinding (somewhat like RP2 pneumatic tubes). Packets are measured in size (in EU/p) and volume (EU). (Size being the amount of energy it contains as it leaves a storage unit, volume being how much energy is left in each packet after inefficient cable usage).
Transformers have two modes - "step up" and "step down". By default, the transformer will be in step up mode when it receives a redstone signal, and step down mode otherwise. This can be changed in the GUI.
In step down mode, up to 128 EU/t can be applied to the 5-dot side of the transformer, and 32 EU/t will be emitted from the 1-dot sides. Step up mode appears to be useless.
When using any Transformer, remember that the 5-dotted side means higher voltage and the 1-dotted sides mean lower voltage. You can change the direction the 5-dotted side is facing by right-clicking a 1-dotted face with a Wrench.
Converting to LV:
In order to convert to LV, you must point the input cable (maximum "voltage" is MV or 128 EU/t) to the 5-dotted side and then link any number of output cables from the 1-dotted side.