Teaching your puppy crate training is the first and best step in his life. It makes all the other steps in his training go so much smoother, much like a solid foundation makes for a superior wall. Establishing you as the Alpha member of his "pack" is one very good reason for starting your puppy in a crate when he is very young.
Another reason for crate training is that dogs love predictability. To know what is going to happen in any given situation makes him happy, and more apt to be the best-behaved dog he can possibly be.
A strong crate is the very basis of good puppy training. A wire crate with a lock is the best kind. Make sure it is large enough for him to stand up and turn around. But not so large that he can roam and wander around. A too-large crate will inhibit house breaking. A crate that is just the right size will be perceived as his "nest", where puppies never "go potty". They will learn to hold it if you do not make a prison out of it.
Never leave a puppy under 8 weeks longer than one hour in his crate. He will soil it, after struggling and suffering as long as he can.
Put a nice pad in there with a bone. Start with placing a tasty treat in there, he will go in and get it. Do this several times without closing the door, let him come in and out freely for an hour or so. Praise him highly every time time goes in, make it all very pleasant.
Then when his attention is on his treat, close the door. Praise him quietly, "What a good boy, it's ok, such a good boy!" In 10 or 20 seconds, no longer, let him out without a word, no praise, just a pat. Do this for increasingly longer intervals, but do not give it a chance to get upset. You can do this several times the first day.
Make sure every training session ends on a happy note, this is crucial.
Once he sees the crate is his own private territory, he will go in there on his own, expecting trips and your attention. When he does, say, "Wanna crate?" with a happy face while getting his fears. Start leaving the room while he is in there for 2 minutes and onward, respectively. When you return, do not make a fuss, just walk over and open the crate. In 3 days he will be officially crate-trained, ready to be left alone for an hour, no longer at first. Leave him gradually longer, slowly and carefully.
Q. Why do I want a crate for my puppy?
A. Because they love it is the best reason. They feel very safe and secure in there. Here are some more:
When you leave a puppy alone, he always has some measure of separation anxiety. This leads him to any behavior that brings him comfort, which is chewing, digging, or when it is severe, voiding his bowels. When placed in a crate, he feels safe because nothing can get to him, nothing can harm him. He will sleep and chew and wait for you to return.
Crate training is the first step in being able to leave him overnight at the vet. Without it he will cry the entire time, feeling lost and abandoned. With crate training, he is sure you will return, you always do. Of course the vet's office is strange and will cause him some anxiety, but nothing like the pure terror he will feel without experience in being locked in.
NOTE: About crate-training, do not make a prison of his crate. Do not use it as punishment. Do not leave him there for more than 2 hours, just time for a long puppy nap and some chew time. After that he will cry. Do not remove him while he is crying. This will make him think he has to cry to get out. No matter what, make sure he is being good when you open the door. He will learn he has to be quiet to get out.
Do not make a fuss when you are letting it out, just quietly open the door and take it out to potty. When he potties, praise him to high heaven! Dogs naturally do not go where they nest, but sometimes it happens. Do not scold, just clean it out with a bland face. He will learn the lesson. If possible, try to clean it while he is outside so he returns to a clean crate.
In 25 years of training dogs, I have never seen any one thing more critical for a dog's well-being than good crate training.