For Christmas, one of my brothers bought another brother mushroom shiitake spawn! It came as dowel rods filled with shiitake mycelium. Most people think of mushrooms as the fruiting body (toadstool), but the largest part of a mushroom is the mycelium (mushroom roots) that colonize a carbon source: paper, wood chips, sawdust, or in this case, logs. 
We cut 3 foot sections of walnut, then drilled holes that matched the dowel rod sizes every 2 inches in three equally spaced columns down the side of each log. Afterwards, we used a hammer to pound a dowel rod into each hole (see below).
This is similar to planting young mushroom fungi into the wood, with the goal of it colonizing the log to convert it into shiitake mushrooms! The key is keeping the log moist, so it has to stay out of the sun and be watered or soaked to keep it from drying out. The last step of preparation is to seal the dowels with bees wax to slow down the drying process as much as possible.
After the log has been fully colonized (~6 months), we will force the log to fruit by soaking it for 24 hours in water, then keeping them around 70 degrees. They should fruit about a week later.
(By the way, the log on Jared’s shoulder is 30lbs!)