SQL Server read xml file data by OPENROWSET

CREATE TABLE XMLwithOpenXML
(
Id INT IDENTITY PRIMARY KEY,
XMLData XML,
LoadedDateTime DATETIME
)

INSERT INTO XMLwithOpenXML(XMLData, LoadedDateTime)
SELECT CONVERT(XML, BulkColumn) AS BulkColumn, GETDATE() 
FROM OPENROWSET(BULK 'D:\OpenXMLTesting.xml', SINGLE_BLOB) AS x;

SELECT * FROM XMLwithOpenXML

1) what is BulkColumn ?

Second Code example

DECLARE @xml XML
SELECT @xml = BulkColumn
FROM OPENROWSET(BULK 'D:\sample.xml', SINGLE_BLOB) x

SELECT
    t.c.value('(PersonId/PersonNr/text())[1]', 'VARCHAR(100)'),
    t.c.value('(Namn/Tilltalsnamnsmarkering/text())[1]', 'INT')
FROM @xml.nodes('*:ArrayOfFolkbokforingspostTYPE/*:FolkbokforingspostTYPE/*:Personpost') t(c)

1) OPENROWSET(BULK 'D:\sample.xml', SINGLE_BLOB) x
What is first parameter called BULK ?
X alias is required ?

Another Code

INSERT INTO CUSTOMERS_TABLE (DOCUMENT, NAME, ADDRESS, PROFESSION)
SELECT
   MY_XML.Customer.query('Document').value('.', 'VARCHAR(20)'),
   MY_XML.Customer.query('Name').value('.', 'VARCHAR(50)'),
   MY_XML.Customer.query('Address').value('.', 'VARCHAR(50)'),
   MY_XML.Customer.query('Profession').value('.', 'VARCHAR(50)')
FROM (SELECT CAST(MY_XML AS xml)
      FROM OPENROWSET(BULK 'C:\temp\MSSQLTIPS_XML.xml', SINGLE_BLOB) AS T(MY_XML)) AS T(MY_XML)
      CROSS APPLY MY_XML.nodes('Customers/Customer') AS MY_XML (Customer);

1) CAST(MY_XML AS xml) what is stored in MY_XML variable ? because alias mention as T(MY_XML)
2) why cross apply is required ? without cross apply we can extract data.

3) to use OPENROWSET any special permission would be required ?

please guide me. thanks