When an item shows as Private on a feedback profile, it means it was a private listing, which is a setting the seller of the item can select and means no item details will show on the buyer or seller's feedback profile. If you would like to make your future listings private, you need to tick the box in the format section (where you choose whether it's an auction or fixed price etc), that says "Allow buyers to remain anonymous to other eBay users". If that is not appearing in the options of the listing form, you will need to click the 'Add or remove options' link next to 'Choose a format and price', tick the private listing option, then save to make it available.
In regards to buyer feedback (that is, your feedback as a buyer), while you can see the item details and prices of items when you are logged into your account, everyone else just sees the feedback comment (the item details remain visible on the seller's feedback profile if FB was left, but the buyer's ID is disguised).
