Normally, there are a lot of devices that can be used as a qr code scanner, such as smartphone camera, webcam, etc. you need to install a QR Code reading program on your device, then it will decode the QR Code.
If you want a good QR code app for Windows I use one called QRCopy. It's got both a generater and a QR code reader (it uses your webcam to scan codes, you don't have to find a way to get the qr code onto your computer first). I tried a few other QR code scanner/reader apps but QRCopy scanned a lot faster and it works in my room which is a bit dark. It does exactly what you asked for, it'll read a code then show the decoded text in a textbox. It can also link up with your clipboard so that it'll decode then put the decoded text into the clipboard, or if you put text on the clipboard it can pop up a qr code containing that text.