Garden centres and hydroponic grow shops sell germination cubes. There are several different brands, but they are all made from a sponge like material which retains moisture but is soft enough to allow small roots to develop and grow. Various materials have been used, including glass wool, coco fibre and synthetic polymer sponge.
Follow the advice on the cubes, normally you wet them with water (some prefer to use bottled water) or buffered water. The seed is pushed about 5mm below the surface. The damp germinating cube is then placed in a sealed sandwich box/bag to retain the moisture. The seeds often germinate within a couple of days, but may take longer.
Out of the best ways to germinate cannabis seeds, germination cubes are one of the preferred ways to get maximum germination rates. Once the seed has germinated the cube is simply transplanted into the next container to grow.