How can i add a new and same type of product (as i am looking) to the site?

How can i add a new and same type of product (as i am looking) to the site?

I've got this problem that I can't solve. Partly because I can't explain
it with the right terms. I'm new to this so sorry for this clumsy
question.
Below you can see an overview of my goal.
I'm using Magento CE1.7
i have a product in my site,I have the same type of product i want to sell
that one here i want to provide that option in my site
for example I have a T-shirt in my shopping site,I have the same type of
product i want to sell my product, for this i want to provide a option
"Sell Same type of Product" in product page....etc
You can see better in ebay.com
i need some ideas about this ?