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I have a very basic law 101 question on codification of statutes and how we refer to them.

For example, The E-Sign Act 15 U.S. Code § 7006 - Definitionshttps://www.law.cornell.edu/uscode/text/15/7006 is also referred to in briefs and online articles as E-Sign §106

The official code is 15 U.S. Code § 7006 correct? So why is it referred to as ESIGN §106? If you can refer me to a website that explains this or can explain here I would appreciate it!

Slightly confused about this too. And I'm a 3L.

Esign is the bill that was passed, which was Public Law 106-229 in 2000. Frequently a big bill is actually codified in bits all over the place in the USC. (Health guidelines here, criminal penalties here, civil cause of action there, building code here, new agency creation there etc.)
If you're talking about the bill as a whole, it's probably in the Public Laws in one big convenient chunk of sections, like 106-229. But if you're just talking about a piece of the bill, you can refer to section 106 of Esign or 15 USC 7006, the code where it ended up.
15 USC 7006 will remain where it is but may be amended by subsequent bills. And Public Law 106 (2000) will always be that exact bill passed in 2000, but may not reflect the current laws on the books.
So which cite you want to use depends what you're referring to and the context.

Rinkrat explained it well. I'd just add that if you're citing the statute using the Bluebook, then you'd indicate both the section of the Act enacting the law and the current cite in the U.S. Code. So ESIGN § 106 would look like: Electronic Signatures in Global and National Commerce Act of 2000 § 106, 15 U.S.C. § 7006 (2012).