Place mobile at the appropriate distance from baby (around 25cm away) and let them enjoy the engaging sound and movement while in tummy time, helping them gradually stay in the position a little longer. When you leave the house, take the mobile along so baby can enjoy the comfort of a familiar toy.
Set the entertainer on tapping mode and let baby try and prompt the fun audio and visual feedback by tapping the toy while in tummy time. This will encourage baby to reach out and try over and over again, strengthening important muscles.
As babies become more comfortable spending time on their tummies, they will be able to lean on one hand while playing and moving the mobile with the other. Make sure to position the mobile within baby's reach.
When babies have mastered sitting up, they can continue to enjoy the toy's features, marveling and the charming sound and lights feedback they create, which will help them grasp the idea of cause and effect, or the fun peek-a-boo window, which will help them understand the idea of object permanence.