"To get started on training your dog to stay, you simply need to make sure to train a sit that's reliable, good and a down, good. If you have that you're ready to get started in your sit stay and your down stay. There's 3 components to a stay, it's duration, distance and distraction.
So to get started I'm simply going to take a little step away, that's a little distance from my dog, Walter. If he gets up I'm just going to recue him into the down and start again, good. And I'm going to see if I move around him a little bit, staying fairly close to him, good. I'm going to add a distraction to see if I can drop some treats on the floor and if he remains, that's wonderful and I'm going to give him those treats. He certainly deserves them.
And duration just comes along for the ride, so as you work on your distances that you can move away from your dog and those distractions ,even marching your feet and your dog remains in a stay, you've got your duration just right there along with you. And once you feel reliable, that your dog is going to be able to manage remaining in the stay position, you can start putting a cue on it.
I like to do something very, very obvious for my dog, like a 1 finger point, good. So you add the cue after you've taught the behavior. Oh you got a little freebie there. Try that one more time, I'll cue it. I'll move and I can even teach him just to get up when I say the word okay and that's how you teach a dog to stay.