Heel, in dog training, means "walk near my heel".
Your dog can heel or the right side or left side. If you walk mostly on sidewalks or paths, right side will keep dogs further away from oncoming walkers, which is a good thing.
If you walk mostly on the side of a road, against traffic, the left side will be safer for your dog.

Why teach heel?
Take the whole puppy program.
These are the basics all puppies need:
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Bonding in human and dog society so they learn to live in both.
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Puppy Potty Training so they learn to eliminate outside.
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Good behaviors to replace bad ones. It's easy to learn 16 words in 8 weeks.
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Socialization so they don't become fearful of new things.
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Leadership so they learn you have everything they need.
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Good habits so other puppy issues don't become behavior problems.

Puppy program options
In your home with the whole family. Each week you'll learn step by step how to teach your puppy new, important life skills.
Multiple sessions. Because puppy brains grow fast, they can learn something new every day. When schedules permit, we can do multiple sessions each week. If you have the time, go for it. You'll have a Super Puppy.
Skip a week. Every two weeks gives you more time to practice, spreads the cost out and if you choose, add a phone consult on the off weeks. This keeps you up to date while saving a bit of money.