UNIQUE/PRIMARY KEY Confusion.

I wrote this stored procedure and it works fine, it seems. The questions I have are as follows:
(1) What is the difference between PRIMARY KEY and UNIQUE. They seem to pertain to the same behavior. When I used only UNIQUE as qualifier I did not see that the column was marked as primary in the SQL Management Studio.
What I need is for a column to be unique in the sense that it would not allow duplicate values and it must have an INDEX on it. I need it to be descending.
(2) Did I do it right or there are aspects in here I do not quite see?

set ANSI_NULLS ON
set QUOTED_IDENTIFIER OFF
GO
ALTER PROCEDURE [dbo].[CreateTableDailyClose]
@symbol varchar (10) = null
AS
BEGIN
SET NOCOUNT ON;
DECLARE @SQL VARCHAR(500)
SET @SQL = 'CREATE TABLE dbo.dailyCl_' + @symbol + ' (
dateTimed DateTime NOT NULL PRIMARY KEY,
opened float NULL,
high float NULL,
low float NULL,
closed float NULL,
volume int NULL,
adjClosed float NULL
)'
EXEC sp_sqlexec @Sql
SET @SQL = 'CREATE UNIQUE INDEX dateTimed ON dbo.dailyCl_' +
@symbol + ' (dateTimed DESC) '
EXEC sp_sqlexec @Sql
END

Thanks.