There is no such thing as a bonsai seed. Bonsai are created by training normal trees. Starting them from seed is a very long term project. I have done it, and from seedling to bonsai pot takes 5-10 years. That maple on the left is probably about 6 years old, the crabapple in the center I would estimate at 20 years old. Growing from seed can be rewarding if you are still young, but don't expect the kind of results in the pictures without a lot of work, planting the seedling in the ground for several years, then careful pruning and wiring. Those instructions are very over-simplified. Seeds like the maple require a long, cold stratification process. I have grown them, but kept them moist in the refrigerator for 3 months prior to planting.

Tips on growing from seed

I see, thank you for your answer.

So now, if I didn't put it in the refrigerator and planted the seeds, but keeping the ground moist, is there something I can do? Mayde buying some kind of fertilizer.. Or put it in the refrigerator with the soil for some time?

Did I destroy the seeds? When should I expect to see the shoots (I planted the seeds in the beginning of the fall) ?

Thanks :)

No fertilizer will help seeds germinate. Without cold stratification some have a chance of making it but most will just rot. I would put them in the refrigerator until about February, and just keep barely moist, not too wet. Remember that you are trying to duplicate nature. Seeds fall to the ground, and sit on top of the soil all winter in the cold and damp. In spring, they are still wet but it warms up and the sun comes out, prompting them to start growing.

So put the whole thing right? With the soil.. the seed is so small I guees I will not find it ;)

Yes, that's about all you can try now.

I would simply sow the seed and leave outside for the winter, they will germinate when they want to.