It's actually very simple to teach come. Basically, you want to teach your dog that coming to you always results in good things happening to him: treats and praise.
Here's how to teach your dog to come:
Inside a quite room, stand six feet away from your dog and call him. When he comes take his collar, click and treat. Repeat this many times.
Gradually increase the distance and the distractions, click and treat each time he comes to you!
With lots of practice you'll get a reliable come!
One very important thing to keep in mind when teaching come is to avoid punishing or scolding your dog when he comes to you. Many people call their dog and when he comes they scold or punish him for not coming quicker. Always make coming to you a positive thing! Otherwise, he won't come, and why would he want to?