Can someone help me do it properly. Customer support doesn't seem to understand what is on the page when you list items and that there is a spot for combined postage discount.

If someone purchases two items, I can send it for the same price as only sending one item - in other words they won't pay postage on second item.  so $1.20 for two

If someone purchases three items, it will cost $2.40 and four item purchased they won't pay postage it will be still $2.40.

Sorry for being confusing but not sure how to word it.