How do I set up to ship only in United States

I was think maybe I only want my cart to ship in the United states.
How do I set it up to work like that?
Well i am not good and not sure about shipping and how it works.
I got it set up to charge a large amount of anyone who orders from another country.
MY Zencart
But it might be better if I just disable shipping to another country all together.

I tried this got 4 items from my cart wanted to check out estimate shipping told me this
Estimate Shipping Costs
Total Items: 4 Weight: 4lbs Amount: $49.00
but when I going to pay it only charged me $10.50 for shipping cost.

Actually the $49.00 was the product cost and shipping was only $10.50 the shipping as 1 item would cost.

it is not factoring in that I have 4 items to ship. It not charging more to ship 4 items compared to shipping one item.

The USPS postal service account is not working at all even though I had set up a account with them.
I think the UPS is working somewhat.
If you give could also tell me what you think about that them questions it would be good..