It’s usually hard to grow bonsai from bonsai seeds. Depending on the kind of tree seed, you may have to chill the seeds first, before planting them in order to get them to sprout.
And once they sprout, it will be many years before they reach a size where you can train them into bonsai tree forms.
It’s much better to go to Home Depot or Wal-Mart, or any garden center, and buy a small shrub or tree (they’re usually pretty cheap), about one or two feet in height, clip its branches and excess leaves to get the desired bonsai “form”, or use copper wiring to bend branches in place. A book on bonsai can show you the different forms or styles and give you instructions on how to prune your small tree.
The best trees for bonsai are larch, maple, pine, elm, birch, and oak. My personal favorite is larch because it’s a tough tree that looks beautiful with the changing seasons. And it doesn’t take long to make a larch tree into an acceptable looking bonsai——this tree is probably only 2 to 3 years old.
http://bonsaijournal.com/images/larchTaper/bonsai_A.jpg