Bokashi is traditionally a fermented substrate such as rice bran or wheat bran, but it can also be made with many other kinds of waste materials such as sawdust, manure, other grain scraps, etc.
It is fermented (kind of pickled) by mixing it with effective microorganisms (EM). It has traditionally been done to make use of the above waste materials, which are transformed into the some of most incredibly beneficial organic matter possible for the garden.
How to make bokashi
Bokashi is made by filling a container such as a 5 gallon pail about 2/3 full with the material, such as sawdust. You can optionally mix in rock dust. Then you make a mixture of EM:Molasses:Water, generally at 1:1:100 (10ml each of EM and molasses per litre of water).
In this liquid, you can optionally mix liquid kelp, fish, and/or sea minerals. This liquid is mixed in with the dry material in the pail until it is moist like a wrung-out sponge, so that is holds together when you squeeze it in your hand, but isn't dripping wet.
You then press the mixture firmly down in the bucket to get the air out and cover it with a plastic bag and then a plate, and even a weight if you have it. It will now only take up perhaps 1/2 of the pail. We want this to ferment without air, like wine, for 1-2 weeks (longer is even better), so there should be no more stirring.
It is better if you can keep it warm somehow, around 100 degrees (40 Celsius). Otherwise, it will take weeks. When it is done, it will smell kind of sweet. It may have white mold on top, which is okay. If you have green or gray molds, it should be put into the compost or buried, as air has probably gotten in and spoiled the batch.
How to use bokashi
The bokashi can then be used as an incredible way to inoculate your soil with these beneficial microbes and organic matter at the same time. It is often used at a rate of only 1 gallon per 200 sq ft. It can be put on top of the soil or dug in.
It can also be dried on a tarp in the sun for a few hours to increase storage time. Dried bokashi is often used to help pickle fruit and vegetable waste in the kitchen. Every time you put the waste into the bucket, a small handful of dried bokashi can be sprinkled on top.When the bucket is full, you can bury the waste a good 12" deep in the garden or compost and because it is infused with these microbes, it will break down very quickly, often in 2-4 weeks. You can even put meat and dairy in the bucket. Bokashi can also be fed to livestock as about 3-5% of their food.
If you are interested in making it, there are some decent videos on You Tube.