This system is simply two stones, a white stone and a black stone, in a bag. Decide at the start which stone is going to represent the answer ‘yes’ for you, and which stone is going to represent the answer ‘no,’ but keep in mind, black is the amalgamation of every color in the spectrum and white is the absence of color. In my experience, black seems to work better as the ‘yes’ stone.
As a modern innovation, and to assist you in learning this method, you may want to include a third stone, which contrasts markedly in color from the dark stone and the light stone. This stone represents the answer, ‘Wrong question. Re-think the issue, and re-phrase your question.’ It can also represent the answer ‘Maybe’ with some questions. You may want to include this third stone for training purposes, especially if you are the type of person who has trouble phrasing their questions as simple yes-no questions or if you are concerned your yes-no questions may harbor some bias which would negatively affect the answer. Otherwise, you may leave the third stone out. I like to stir up or roll the stones in the bag while I am asking my question out loud. I then reach in the bag with the index finger of my non-dominant hand and draw the first stone my finger lands on.
My normal rule for most divination methods is, ‘No more than three questions of one divination source in one sitting.’ Every divination tool or method has its own ‘guiding spirit’ and you don’t want to test that spirit’s patience. Too many questions in one sitting with some divination tools, then the spirits of those tools start messing with you and start giving you bad or horrible answers to get you to knock it off and leave them alone. The I Ching will even tell you, when you ask it a third question: “You are becoming impatient. I do not instruct the impatient.”
With the Yes and No Stones, that rule of thumb doesn’t apply. With this divination tool, you have to ask multiple questions, and it works best when you have a specific subject or topic you want to ask about. I recommend composing a list of questions before starting to consult the stones. That way, you can think through just what information you are seeking. Just be aware that an unexpected answer may trigger a sudden new question which is not on your list. Let me try to give you an example.

Hello and thank you very much for your posts which are really handy and well done. The 2 stones divination system really enjoyed me and I feel like this is something I can use. The only question is what kind of stones should I use ? I guess Onyx for the black one, but what about the white and blue one ? What should you recommend ?
Also it is not mentioned in your post but during session do you use a candle lit and incense ?
Thank you
I actually use the sort of glass stones that are used in vases with floral arrangements. Because the glass stones are made to be roughly the same uniform shape, my finger can’t identify which stone I’m grabbing, so I know I’m not deliberately grabbing a particular stone for the answer.
But if you want to use natural minerals, I’d say either moonstone or some other white stone like snow quartz for the light stone. Onyx, most obsidians or jet would all be good choices for the dark stone. The third stone can actually be any other color. Either Lapis lazuli,or a certain shade of turquoise stone would be lovely blue stones to use for this purpose, but a red jasper or a green agate would also be nice for the third stone.
I don’t normally light a candle or incense when using the yes-and-no stones, because sometimes, I’m consulting them on the spur-of-the-moment. I think it is good preparation to light a candle or incense if you have a whole list of questions which you want to put to them. In that case, I think lighting a candle and/or incense helps to focus one’s own mind on the seriousness of the consultation, and it can help to summon the spirits you are asking to communicate with you via the stones. I hope this helps. Sorry for the tardiness of my reply.