if you have a laptop with a hdmi output, you can run a hdmi cable out to a tv, if it has a hdmi input, and once you get espn3 on your laptop, you change your tv input to match where you plugged the cable and you can watch the game on the tv.
Espn3 may want proof you are a comcast subscriber, you simply enter your account number and password that you use to enter your comcast internet site. If you have no user account, sign in and get one. Do everything step by step. Key no.1 is to have highspeed internet available, either lan or wifi.