Can any one explain about Coalesce()?

Question

Can any one explain about this statements?

• The Coalesce() function returns the first non-null value among its arguments.
• The COALESCE() function is based on the ANSI SQL standard whereas ISNULL function is a Transact-SQL function.
• Can any one explain about ANSI SQL standard and Transact-SQL function.
• An expression involving ISNULL with non-null parameters is considered to be NOT NULL, while expressions involving COALESCE with non-null parameters is considered to be NULL.
• If we use more than two parameters with the ISNULL function then we must use nested ISNULL functions.
• can any one explain nested ISNULL function
• The ISNULL() function looks at the first value and the second parameter value is automatically limited to that length but COALESCE() does not have this restriction.