For activating a device with Netflix, you'll first need an account. The Netflix activation page will ask for username and password if you already have an account, or recommend that you signup for their service if you're not a member yet.
You'll only need one Netflix account for all of your devices. In fact, you can activate and connect as many devices as you want to your Netflix account. Depending on the membership you have, you'll be limited on how many devices you watch simultaneously with Netflix service.