I don’t know what a “Product Key” is and I don’t know how to activate Windows 7. Can someone please help me?
you can use windows loader to activate your windows
If you have the serial then you can just call the automated line at microsoft to activate it. if its on more then one pc just tell them its only on 1 pc..
Is the computer new or older? Did you purchase Windows 7 or did your computer come with Windows 7? The product key is 25 digits, both letters and numbers, that would let Microsoft know about the installation and licensing for Windows 7, if it is a legitimate product key or a stolen/pirated key.
When you find the product key, which either is in the packaging of a store bought package; on the back, side, or bottom of the computer; or in an email if purchased and downloaded online, just enter the product key when prompted and the process will guide you through to activate Windows 7.
An example of what the sticker should look like that would have the product key can be found here: http://www.microsoft.com/oem/en/licensing/antipiracy/Pages/COA_hologram.aspx?sid=e9KWlSWb4Euqt7A7Bztnew#fbid=j18uN0_yCau
See Wouter R answer, maybe you purchased the pc with windows in trial mode, in this case you have to buy a serial, it is important since an upgrade to windows 8/8.1 will replace you old windows 7 license
If you bought the PC with Windows there should be a sticker from Microsoft on the PC, usually on the back of a PC or the bottom of a laptop. If you bought Windows separately the key should be inside the box.