explain this sql query [Resolved]

CREATE PROCEDURE [dbo].[AddNewFiles]
(
  @CategoryName varchar(50),
  @FileName varchar(50),
  @FileCost money,
  @Description varchar(200),
  @FileLocation nvarchar(MAX),
  @EncryptFile nvarchar(MAX)

)
AS
	BEGIN TRANSACTION 
    IF NOT EXISTS (SELECT 1 FROM Categories WHERE CategoryName=@CategoryName) 
    BEGIN
        INSERT INTO dbo.Categories (CategoryName) VALUES (@CategoryName);
    END

    DECLARE @CatID int
    SET @CatID = (SELECT CategoryID FROM dbo.Categories WHERE CategoryName=@CategoryName);
    INSERT dbo.FileDetails (CategoryID, FileName, FileCost, Description,FileLocation,EncryptFile) 
    VALUES (@CatID,@FileName, @FileCost, @Description,@FileLocation,@EncryptFile );
    COMMIT TRANSACTION 
GO

[Resolved]