difference between Property & index function?

The Property() function is used for accessing fields or properties of a data type.

The Index() function is used for retrieving elements from a list or array based on their position.

For Example: 

a!localVariables(
  local!employee: a!recordType(
    field1: "John",
    field2: "karthik"
  ),
  local!employeeList: {"Alice", "Bob", "Charlie"}
),
a!section(
  a!textField(
    label: "First Name:",
    value: property!employee.field1
  ),
  a!textField(
    label: "Second Name:",
    value: index(local!employeeList, 1)
  )
)

The Property() function is used for accessing fields or properties of a data type.

The Index() function is used for retrieving elements from a list or array based on their position.

For Example: 

a!localVariables(
  local!employee: a!recordType(
    field1: "John",
    field2: "karthik"
  ),
  local!employeeList: {"Alice", "Bob", "Charlie"}
),
a!section(
  a!textField(
    label: "First Name:",
    value: property!employee.field1
  ),
  a!textField(
    label: "Second Name:",
    value: index(local!employeeList, 1)
  )
)

My respect for replying to a six year old conversation, explaining the same topic a fourth time.

There is a small mistake in your code snippet. A "property!" domain does not exist in Appian.