The blocks are used in some educational electronics kits, such as the Gakken EX-150, to allow experiments to be performed easily and safely.
Most blocks contain either a single electronic component, for example a resistor, just some wiring or both.
On the sides of each block are conductive metal strips, so that when two blocks are placed side-by-side, their metal strips touch allowing electricity to flow between them.
A circuit is built by placing a configuration of denshi blocks in a two dimensional grid.
The instructions for building the circuit need only illustrate where to place the blocks in the grid.