Your puppy's first collar should be one with a buckle or snap closure. Never use a chain or choke collar. It should fit with enough slack to get two fingers in between the collar and his neck but not loosely enough to slide over his head. Be sure to check the size every few days, since puppies can grow very quickly in a short time.
You can help your puppy get used to his collar by initially making him wear it for only short periods of time. If he seems uncomfortable or struggles and scratches at it, don't be concerned; it should only take a few days for your puppy to get used to having it on. When he begins to ignore it, you can leave his collar on all the time.
Once your puppy is used to his collar, you can attach a leash. To help him get used to the feel of his leash, let him drag it around during a few play periods. You can pick up the leash now and again but keep still when you do. That way, your puppy will learn that being on the leash means he can't go wherever he wants to because he's attached to you. Once your puppy has accepted that he's restrained, give plenty of praise before letting him go again.
Remember that your puppy can easily get lost, especially in his early weeks, so it's important that you attach an identification tag to his collar. This tag should include your name and contact information.
You can further help to identify your puppy if he becomes lost or is stolen by getting him a microchip implant. A microchip implant is an effective and easy way of linking your puppy to you and involves the simple insertion of a tiny integrated circuit the size of a grain of rice under your puppy's skin. Using an RFID scanner to read the microchip allows animal shelters and animal control centers to quickly identify lost pets and reunite them with their owners. Please refer to the section on microchip implants for further information.