No matter how you choose to use the crate, ensure your puppy is entirely comfortable in it before leaving him inside. Sit next to the crate with your puppy inside and gradually build the duration and distance away from you. If you lock him inside for longer than he's ready to tolerate, he will view this as a negative experience and may avoid confinement in the future. Go at your puppy's pace, and never hesitate to take a few steps back in the training, so he'll be comfortable and ready to move forward.