I outsourced today's lesson. You'll understand after you see it.
Here's a video showing extremely good play skills. Four specific techniques are demonstrated; running away without holding the end of the toy (chase), "tagging" the dog and running off, running with the dog while holding the end of a toy, and playing tug after falling to the ground. All excellent games to play with a puppy. The purpose of the toy in Lyra's mouth is to keep her from chomping legs and clothing. Ideally, she'll outgrow the need for a toy in her mouth and she'll be able to run and play without it, but for now, she's learning how much fun it is to run and play with humans.