I don't understand the latter part of the sentence ...

You need to be more explicit about what part of the sentence you have failed to understand. You're not going to get an answer unless you are more specific about the part which confuses you.

Well, apparently this company, called "Square", has a device that can be attached to the computer or phone. It can accept credit cards.

But you have all the information, so I don't really know.

I'll just wait for the loop to close.
possibly VM

sorry，I don't understand the word "tablet" in the sentence, and "swipe a card through a slot ", thanks!

a tablet in this context is a flat portable computer.

swipe a card through a slot.
Do you have credit/debit cards in China?

I saw one of these in action last weekend--it's very cool.

In the US, pulling the credit card thru a card reader is called "swiping the card".

This reader looks like a square of white plastic, maybe an inch and a half on a side, and maybe a half inch deep, with a slot thru it lengthwise. and a plug on the other side that you plug into the jack on your smartphone or tablet computer. It's basically a very small cardreader. You download the application, plug it in, and process the credit card wherever you are, the same as processing a credit card in a store, except the reader is very small and the phone/computer isn't connected to a phone line.