A factory reset will return the computer to "out of the box" state. This means that it will have whatever originally came on the computer. If your 'Microsoft 10' (I'm assuming WINDOWS 10) was installed afterward, then yes, you will need that to reinstall. if the USB stick only has the activation number (Again, assuming you meant Installation KEY), then yes, you will need to enter this number in order to get the installation activated.
Always save any and all personal information on your computer to USB, CD, or DVD before performing a factory reset. You WILL lose all information you have added to the computer: files, spreadsheets, pics and any and all programs you added after. (Copy any downloaded install programs to removable media too)