an item

An "item" is basically just a thing. The word "item" usually means one thing in a list or a group.

The things that are sold in a shop, an online store, etc. can be called "items":

I got it from a store that sells all kinds of art and handmade items.

A new law requires that fast food restaurants label each item with the number of calories it contains.

(something) ships for free

"Shipping" something means mailing or sending it to someone.

You usually don't use the word "ship" to talk about sending a paper letter, and certainly not for sending an e-mail. You "ship" things like packages or even large containers of materials for factories or warehouses:

How long does it take to ship something from the U.S. to Europe?

When a business sells things online or in a magazine, they usually give details about how or when it will be sent to you like this:

This item ships in 2-3 business days.

All packages ship via FedEx.

If the website or advertisement says this:

This item ships for free.

...it means that you don't have to pay extra money for the company to send you the item. You just have to pay the price that's listed.