You wouldn't walk through Times Square with your bank account number and PIN written on your T-shirt. So why would you start browsing the web on your new laptop without virus and malware protection enabled? Your new notebook almost certainly comes with a free 30- or 60-day trial of a popular security suite, but if you want to take advantage of that trial, you need to register. Registering typically involves providing your credit card number so that you can be billed for a monthly subscription if you don't cancel by the end of the trial period.
If you want to save money and avoid nagging ads, you can uninstall the pre-loaded antivirus program and install , which is not as comprehensive as some paid suites, but is free for life. Download it at www.microsoft.com/en-us/security_essentials.