Puh.. with side? Good question. Never seen such stone before. I think you will have to try and see if the Stone has different grids. I assume that the yellow one might be the standard side and the other might have been colored.
However, I would always Lapp a used stone when getting it. Take a pencil and draw some diagonal lines all over the stone. Than take a fine whet sanding paper. Lay the paper on a lean surface and Lapp the stone one the sanding paper. Best way is to lead the stone in 8-Stokes (like drawing eights on the sanding paper). After some stokes take a look if the pencil lines are all eliminated. Perhaps the lines will stand to go on the corners of the stone . That’s what usual happens with used stones, because they became a bid concave from the former unse. If so, continue until all pencil lines have gone. Finally make again some lines and make the same procedure wir a finer sanding paper (around 1000 grid). Once all lines have gone you can expect that you have a lapped stone and can put your razor up.
How may stokes you will need is hard to predict. I do not even know if this is really a finishing stone. If your razor is Stil sharp and need only a refresh, make 10 double stokes (alway front one side, back the other side, to be shire that you will not get a burr. Test the Edge on your arm hairs and if you find the feeing sharp and. Smooth, start stropping on a leather strop about 100 double strokes. If the edge is worse than before (more crispy, not keen) the stone is probably not a finisher. If it’s better, continue shaving.
There is also an instruction how to use it. I copied the translation of the instuction from the thread.
"1- Put on the Gillot stone "a" a thin layer of dry soap. Pass the blade on the stone several times with a rotating movement. After repeating this operation several times, do it again on the other side of the blade.
2- After this operation, put some drops of water on the stone, repeat the movements with the same method, then do it again on the other side of the blade. Finish on a strop."
I will probably try it in the not to distant future.