How do you train a dog to go, lie down, stay and how to walk on a leash?

My grandparents have an Airedale, so he is a rather smart dog i taught him sit within a matter of minutes. I would like to teach him to go, lie down, stay and how to walk on a leash without pulling them over. He is pretty young and rambunctious he is also very very strong.... he also scares very easily. also, how do i get my grandparents to reinforce the training when i leave?