“Into” means to enter (entrar en), or to go inside a room or place, and one can also “get into trouble”.
- “Mr. Obama walked into a tree”
Grammatically yes, although getting inside a tree (entrando en) would be quite exceptional or difficult, even for the President of the United States. The correct form would be “Mr. Obama walked in to (chocar contra) a tree”.
“Onto” does not exist. If you wrote: “The Spanish King put his crown onto the table” you have made an error. “On to” would be the correct form.
So avoid getting into trouble by never using “onto” – instead use “on to”.