This is a free service usually offered to those who already pay for TV. If you don't pay for TV, and NBC is walling off the content to those who pay, you will not be charged for logging in. The most that will happen is, you'll get an error message saying you don't subscribe to TV.
Alternatively, if you have another pay TV provider in, such as your local Cable company or a Satellite provider, use the option for that pay TV provider instead of Verizon.