Yes, you need to actvate your Windows O.S. within 30 days of installing, or it will quit working properly. When it asks if you want to activate Windows, click on the affirmative answer. It will have a drop-down box of several different countries. Highlight you country (U.S.) and it will give you 2-3 numbers to call. You will probably want to call the toll-free number. You need to be in front of your computer. The process is quite simple and shall only take 5-10 minutes.
I always activate by phone, because I've had to reactivate the same computer several times, and if I do it over the internet, it will say I've done it too many times and won't let me proceed.