Your question is not very clear, but you can basically achieve this in 2 ways, client side or server side.
Client side needs a array or similar that stores a list of the product ids and info, the server side might use a session object, or a table in the database if you want persistent shopping carts.
There are many examples on the net of implementing carts, so i suggest you search google.
http://lmgtfy.com/?q=asp.net+shopping+cart+tutorial[
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You need to then display the shopping cart, by binding to a db query or the object you created, or by manual iteration of the array and gridview updating.