Usually sellers will include eBay fees in the price of the item.

Then any packing and handling costs are added to the price of postage.

Or some sellers include it all in the price of the item and list with free postage.

But it's up to you, some sellers prefer to add any pack n handling to the price of item as well and charge exactly the postage price only. Because some buyers when they get the item see a postage price of $7.50 on the package and then complain that they paid $10 not realising it is also for pack n handling.

But as I said, it's up to you how you factor the costs into your listings.

P.S. We were all newbies at some stage.