If you want to generate a new Guid (uniqueidentifier) in SQL server the you can simply use the NEWID() function.
Example
SELECT NEWID()
GO
— This will return a new random uniqueidentifier e.g.
E75B92A3-3299-4407-A913-C5CA196B3CAB
To select this Guid in in a variable
–assign uniqueidentifier in a variable
DECLARE @EmployeeID uniqueidentifier
SET @EmployeeID = NEWID()
You can directly use this with INSERT statement to insert new row in table.
— Inserting data in Employees table.
INSERT INTO Employees
(EmployeeID, Name, Phone)
VALUES
(NEWID(), ‘John Kris’, ’99-99999′)