Most people never stop to think about where trees come from. In nature, almost all trees have been grown from seed. It is actually quite easy to grow most trees from seed. Some are a lot easier than others and some take a lot less time than others. For the beginner, I would recommend species that either requires no stratification or a short stratification period. I would also recommend species that have a relatively simple scarification, such as a 24 hour water soak. These seeds will germinate quickly and then just need plenty of light and warm temperatures to grow.