Most (all?) modern computers come with a NIC (network interface card) they do sometimes go bad and you can go to your local computer store to get one that you can install in your computer. As Dogman noted you will need to contact your local ISP (internet service provider) to get a connection to the Internet.
How old is your Pavilion? If it is like a Pentium 3 model or something, you may not have an internet card. If it is made in the last 5 years... there is like a 90% chance you've got one. Just call your local ISP... the phone company or the cable TV company. If you don't have a card inside, they will usually give you one for free as long as you keep the service for 6 months or more!