One fun way to germinate the seeds is to put them in a zip top bag with damp paper towels. Then you can actually watch them germinate. All of the food that the plant needs to sprout is inside it, it just needs water.

Sprouting will probably take a few days. Then you can move the sprouts to larger containers. A small plastic food container will work. Have an adult help you punch some holes in the bottom. This will let any excess water drain out so that your plant doesn't get soggy. Then put that container on top of a waterproof plate or lid to catch the extrawater. Then put potting soil in the container. You can use regulardirt, but sometimes it doesn't have all the nutrients the plant needs.

Your plant will have to make its own food from sunlight after it uses upthe food inside the seed, so it will need sunlight. You will need towater it too.

You can sprout all kinds of seeds. Ask if your family has bean or peas(the dried kind, not the cooked and canned kind) that you can sprout.

Alders need to be able to grow with their roots submerged, at least during life. I don't know what their sproud conditions are, but plant them along a stream and they might grow there (that's normally where alders grow). The sycamores also grow in those stream channels, although not quite as close to the stream itself since their roots don't need to be prepetually underwater.

The best source of immediate data on germination of North American tree seeds is the US Department of Agriculture Handbook 450 " Seeds of Woody Plants in the United States" - which is at least into its second edition.

Fresh (this season's) Alder (Alnus) seed may be germinated immediately. Planting depths are recommended between 1/8 and 1/2 inch. In some cases a hole is made in the earth and either sand or vermiculite has been placed in the hole, adjacent to the seed. Dried seed often has gone dormant and has to be subjected to "stratification", that is, prolonged low temperature, in order to break dormancy. Stratification generally involves placing in a refrigerator for 30-60 days at 34 to 41 degrees, although in another separate study they suggested 180 days at 41 degrees.

I note that the seeds discussed here are from species of Alder from colder climes, and our local Alder (Alnus rhombifolia) may need no stratification.