For years, using a crate has been perceived by some as a cruel way to treat a dog. Many are under the impression that everyone who uses a crate for their dog simply leaves them in a cage for untold hours. Nothing could be further from the truth! In fact, when used properly, your pup will come to see his crate more along the lines of his den and be happy to spend time there. Bear in mind, not all labs respond to a crate in the same way. Some might walk right in and make themselves at home, while it's going to take a little extra work for some to be comfortable.
The big thing is to take your time and to give your dog plenty of time to become comfortable with his new "den". This way you should not have a problem leaving your pup in his crate during the day while you are at work or at night while you are sleeping as needed.
For a dog in the wild, his den is his safe place, somewhere he goes to be secure and comfortable. He will raise his family in his den, rest in it, and bring his pack into it for safety when needed. Your pup will draw on this natural instinct and come to see the crate in much the same way if you take your time and follow through on his training. The most important part of the training process is to do your best to help your pup to see his new crate as his den. The more comfortable you make it for him, the more likely he will be to enjoy going in it.
Crate training starts out with buying the right size crate. Since your pup is going to eventually grow into a full-size Lab, you might be tempted to buy an adult-size crate for him. This might work if you are able to put a partition or temporary wall in it to make it smaller to start out. If not, you should start out with a crate that fits your pup. This will help make things go easier. Along with this, you need a few things:
Since you are training your dog to stay in a crate with the door locked, which is something he may not like at first, be ready to take your time. All good things come to those who are patient.