On Yorishiro
Image Source: Daihou Hachimangu
A yorishiro is a vessel in which kamisama can be called down into and reside, temporarily or longer-term. Examples of this include shide, rocks (especially large ones), islands, and so on. Most Japanese laypeople do not make yorishiro because they have access to shrines distributing ofuda, but for a lot of overseas Shintō practitioners it is a good alternative when obtaining an ofuda is difficult. To be specific, this should only be done when you have no way of obtaining an ofuda for the kamisama you would like to worship. Even then, you can practice 遥拝 yōhai, which is to pray in the direction of the shrine you would like to pray at. Ofuda are always the best option. This is also very different from making an ofuda, which should never be done by a layperson.
What is a yorishiro?
The Kokugakuin University dictionary defines it as follows:
The place (or object or person) inhabited by a kami's spirit when it descends for a religious ceremony or when possessing a person. Yorishiro may be natural objects such as trees or rocks, or implements prepared for use in rituals, such as pillars, banners, or ritual emblems called gohei. In those cases in which a human acts as a yorishiro, he or she is referred to as yorimashi. Yorishiro may also be called tsukawashime or osakigami ("servant familiars") based on the concept that kami may possess and use feral dogs, wolves, monkeys, and birds as their familiars. Ancient forms of yorishiro include himorogi (divine trees), iwasaka (rock cairns), and the various hand-held ritual implements generally referred to as torimono. In particular, the rituals at himorogi and iwasaka reflect the belief that kami make their presence known in ritual sites with natural forests, groves, and rocks; this belief led to practices such as erecting trees in ritual sites and decorating them with objects into which the kami might descend. Many different forms of yorishiro exist, ranging from the large cones of sand seen in the Miare shinji of the Kamo Wakeikazuchi Shrine, to the "heart pillars" (shin no mihashira) of the Grand Shrines of Ise, the log pillars (mihashira) seen in the Onbashirasai of the Upper and Lower Suwa Shrines, the shibasashi of the Usa Hachiman Shrine, and the ohake or osashibō used at local shrines to mark the house of the lay priest for that year (see tōya).
How to Handle and Create a Yorishiro
A yorishiro is treated with the utmost care and respect. Your hands must be clean when handling one, and you should try to be clothed in not-pajamas (not necessarily formalwear -- just clothes that are what you'd wear normally). You can use a mirror, such as the ones commonly placed on kamidana (that are purchaseable online) or use a stone and other such natural item if that makes sense to you. Make sure to purify it before placing it on your kamidana, and to remember that a yorishiro cannot be repurposed once consecrated. For purifying the item to be turned into a yorishiro, you may chant Ōharae no Kotoba and sprinkle salt on it.
How to Create a Gohei
A gohei is a paper and wood yorishiro that is often seen at shrines, but is appropriate for home worship as well, especially if you are unable to access an ofuda. It is important to do this with clean hands and in a clean setting.
Here is some footage of a person folding some gohei. The knife/scissors etc. you use to cut the paper should be dedicated to this purpose. Rice paper is cut and folded into a specific shape (known as shide), and the wood holding the paper (heigushi) should be wood or bamboo. It seems that most people recommend securing the shide onto the heigushi with clean or pure hemp string. @livingwithkami advised me that some clergy specifically advise to use knives (i.e. X-Acto knife style knives) and cutting mats instead of scissors. It's also worth noting that both these videos do treat the paper a little roughly. If you make a mistake, you must start over again from the beginning. Create gohei with a sincere and pure heart, and keep in mind that this is an item that is for kamisama -- this is why so much care goes into making it.
Some further photos of gohei creation from Kino Atago Jinja
Similarly, but from Tsurugamine Kumano Jinja
A handy diagram on the first two pages here
There are different shapes for some kamisama, but a lot of this can depend on the shrine or family, etc. This simple lightning shape is almost universally used and therefore I recommend it the most.
Enshrining a Gohei
Enshrining a gohei is not too dissimilar from enshrining an ofuda -- make sure it stays upright on your kamidana. There are stands for gohei to this end that you can purchase online or make yourself. Other than that, standard protocols apply.
