This video demonstrates how to handle your puppy into the sit, down and stand positions. It's important that the puppy get used to being touched and handled in ways that he might find objectionable later.
Just as we handle our puppies so that they are relaxed and comfortable when being groomed, examined by us or the veterinarian, we want to accustom our puppies to handling they will receive later in their training.
This exercise is not meant to teach your puppy the commands of "sit, down and stand." However, it facilitates the process of teaching these commands and will be used more extensively with more advanced obedience commands as is demonstrated in the relevant video.
Start when your puppy is relaxed and perhaps tired from a good play session, but not so tired that he is sleepy and unable to concentrate on the training. Use lots of praise and reward and even food treats. End each short session with a little play time or cuddling or whatever your puppy desires at the moment. When your puppy is fully accustomed to the handling, then you can practice it anytime, anywhere, even when your puppy is on the rambunctious, energetic side.
Gently place one hand under the puppy's belly and support his shoulders and chest with your other hand. Then while supporting his chest, use one hand to gently tuck his bottom into a sit. If he springs right back up, just tuck again and again until he understands what you want. While the puppy is sitting, gently slide his front legs out from under him to bring him into the "down" position. You might have to use one hand to keep his bottom from springing up.
With repetition, praise, rewards and treats, your puppy will soon understand what you are requiring him to do or accept and he will not mind it at all.
If at any time the puppy tries to bite you in protest or wants to turn this into a game of wresting and biting, simply switch to the no-biting exercise including the cradle and chill, then resume the body position handling exercises.