I suspect there is a language misunderstanding here. An "Old World" turn of phrase is to call a seed a stone. In particular, for "stone fruit" the seeds of various members of Prunus are referred to as stones. I believe the OP is asking how to grow lemons from seed. I am assuming English is not the OP's first language.
Poland is a temperate climate country, with winters that compare to the Midwest USA. So the question is about how to grow and develop a lemon tree in a container. And I assume since the question was asked on a bonsai forum, @BPW
is probably looking for a more bonsai orientated answer to his question. Since winters are cold in Poland, citrus trees will have to be grown in pots, either as for bonsai, or nursery style pots. The plants are normally put outdoors for the summer and brought indoors when frost threatens. Returned outdoors in spring after danger of frost has passed.
To grow lemons from seed, simply collect seed from a few lemons obtained from produce market. Most culinary citrus have a fair percentage of seed that are apomictic parthenogenic, meaning that a fair percentage of the seed will produce a plant fairly similar to the parent plant. In other words, seed from a lemon, will give you lemon trees that will produce fruit fairly similar to the lemon the seed was collected from.
Citrus seed, lemon seeds, need to be kept moist from the time you collect them until they are planted. Drying out will kill the embryo in the seed. Wrap seed in moist paper until you are ready to plant the seed.
Use a clean soilless potting media. In the USA a blend of pumice and coir, or pumice and peat is a common seed starter mix. Peat, Coir, Perlite, Pumice, Vermiculite, fine bark, and a fair number of other substrates make for good seedling starter potting media. Usually a blend of 2 or more of these components are used. Single component mixes are usually avoided. I like perlite & peat mix, roughly 50:50 or a peat & pumice mix, again 50:50.
The initial pot for starting the seed should not be overly large. A 10 x 10 x 10 cm square pot would be fine for a dozen seeds. Fill pot with mix, tamp the media. Then place seed on surface, then cover seed with roughly 0.5 cm of additional potting media. Then water the pot, to thoroughly wet the media. Then set the pot outdoors, in full sun will yield the strongest seedlings. Indoors growth will be weaker because the light intensity will be less.
Keep pot with seed moist. In a week or two, new seedlings will become visible as they sprout. You may fertilize lightly after the second set of leaves appear on the seedlings.
Good luck. This process is not different than starting tomatoes or other vegetables from seed.