Sadly, things don't go according to plan. The puppy knows his job just fine and wants to play in that floppy eared, pounce-and-box-his-face way that puppies do. The trouble is the established dog is none too thrilled about it. In fact, he's downright grumpy about the new addition. So far he growled and grumped, shown his teeth and snarled, but not actually gone as far as snapping at the new bundle of fun. Oh dear, this isn't how you planned things at all.
You're fairly confident the older dog wouldn't actually hurt the newbie, but still, this tension wasn't part of the plan for one big happy fur family. In fact, you're wondering if you made the right decision since all that's been achieved is making the older dog miserable.
Now the older dog is no longer the center of attention. To make matters worse he's expected to put up with having his face boxed and tail pulled. Then there's how the upstart steals his food, bed, and favorite toys.
Helping an older dog accept a puppy has a lot to do with getting into the mind of the established dog, and understanding how he sees the world. This enables you to minimize the disruption to his life so that he feels less threatened and can open his heart to the youngster. This involves making sure each dog has his own resources (food, water, bed, and toys) and you acknowledge the older dog ahead of the puppy.
In addition, you can use reward-based training methods such as clicker training, to reward the older dog when he uses an appropriate coping strategy, such as getting up and moving away from the annoying pup, rather than growling.