I have several products. Is there a way to just sell one of them? In other words have the "add to cart" function on one product?
I guess you have to explain a little bit more in detail what you want.
The simple answer is, yes, you can have several products and sell only one of them.
One way would be to use different layouts for the category page (sublayout products.php) and the productdetails page (productdetails view, probably default.php).
You could also not add any price to the products you don't want to sell, so the AddToCart-Button won't show.
Regards
Stefan