1NF:

Employee	Age	Department
Melvin	32	Marketing
Melvin	32	Sales
Edward	45	Quality Assurance
Alex	36	Human Resource

2NF:
Employee (EmployeeId*, EmployeeName, EmployeeAge)
EmployeeId*	EmployeeName	EmployeeAge
1			Melvin			32
2			Edward			45
3			Alex			36

Department (DepartmentId*, DepartmentName)
DepartmentId	DepartmentName
1				Marketing
2				Sales
3				Quality Assurance
4				Human Resource

Employee_Department (EmployeeId*@, DepartmentId*@)
EmployeeId	DepartmentId
1			1
1			2
2			3
3			4

2NF Example:
product_brand (pbID*, productID@, brandID@) 	Application logic must stop duplicate
												product/brand entries.
product_brand (pbID^, productID*@, brandID*@)	Use composite key
pbID	productID	brandID
1		1			1
2		1			2
3		2			3
4		3			4
5		1			1 (OK without app logic) (Would be dis-allowed w/ composite PK)