"Each" and "every" basically mean the same thing. But people use them together in the phrase "each and every" when they want to emphasize the idea of "every" or "each". It's also a little more common in speeches to large groups of people than in one-on-one conversation. For example, you can say this to a group of employees:
I want each and every one of you to come up with a list of five to ten potential customers. Who should we be pitching this to?