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 can be used to transform many packets of 32 EU/t to less packages of 128 EU/t.(small packages enter from the dots and the bigger one exits drom the 5 dots) this can be useful when carrying packets for long distances as every package loses eu with each cable passed, meaning the more packages you have the more EU loss you'll have, making 1 big package more efficient than 5 smaller ones
See: Crafting Guide
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.