Blocking compost is readily available from any garden centre or you can make your own mixture (as long as you ensure it is free of weed seeds / disease). It is best to wet your mix some hours before you make the blocks. You will find that the penetration of water into the planting medium is much better if you do.

Wet the mix thoroughly into a slurry-like consistency
(avoid galvanised metal tubs and use plastic instead)

Press the soil blocker into the compost 2 or 3
 times to fill the block chambers

Scrape the blocker across the side of your mixing tub
to remove any excess compost from the bottom
of the blocks

Depress the plunger to eject the blocks

Each block has a small indentation for accepting the seed. The seed will sprout on the surface of the moist block. No water is needed for the first 3 days but after that use a fine spray from a hose or a hand pumped mister. After a few days, also add a small amount of nutritional support.