Windows 8

No you can't. Each computer must have its own upgrade license and the one on the flash drive is only for one computer--the first one it was installed and activated on. If your friend already used it once on his own computer, the installation on the laptop you have will not be activated and cannot be used. Also--You cannot install it on another computer.

You can install it on another computer but it would ask for another product key which you would need to buy.

To get the media to create a USB flash Drive (in case you need to reinstall on your current computer) you can obtain your current product key with Belarc Advisor and download the media from Microsoft.

This is explained in my wiki A Clean Install of Windows 8 Step 2.

Once you have the product key go here and select install Windows 8

For the US: http://windows.microsoft.com/en-US/windows-8/upgrade-product-key-only

For the UK: http://windows.microsoft.com/en-gb/windows-8/upgrade-product-key-only 

Insert your product key when prompted. You should then begin downloading the files and get the option to make the .iso and bootable USB. As on page 73-77 of the Windows Reinstallation Guide/A Clean install of Windows 8.

Next to install Windows 8 on your other laptop using this media you can use one of the following product keys:

XKY4K-2NRWR-8F6P2-448RF-CRYQH (Windows 8 Professional)
RR3BN-3YY9P-9D7FC-7J4YF-QGJXW (Windows 8 Professional with Media Center)
FB4WR-32NVD-4RW79-XQFWH-CYQG3 (Windows 8 [Home])

Pick the one that matches the version of Windows 8 you downloaded and made the bootable USB from.

These keys are trial product keys and you can use them for up to 120 days.

This should give you enough time to evaluate Windows 8 on your other machine and purchase a license if you like the way your other system is running.

 The rest of A Clean install of Windows 8 will help you.