multiple sizes/prices for each product

Not sure how to add a shopping cart to a product that has multiple sizes/prices where a customer can choose which size. Do I put a cart after each size?
Ex: Salve 1oz. $8.00 2oz. $16.00 4oz. $30.00
I’m really new at this having to research everything I attempt to do on wp & don’t know all the terms, so please keep it simple
thanks

http://wordpress.org/extend/plugins/wordpress-simple-paypal-shopping-cart/