When you apply for a new Visa credit card and are accepted, you need to verify the card before you can actually use it. This verification process allows Visa to know you received the card in the mail. Without verifying the card with Visa, the card cannot be used and if you attempt to purchase something with the card, no matter if its online or in person, you are going to be declined.
Wait for your Visa card to come in the mail. It is going to arrive in an inconspicuous envelope and probably won't say anything about "Visa" on it.
Remove the new credit card from the packaging. There is a small sticker on the front of the card with a verification number on it.
Call the number. You won't actually talk to an individual while verifying your credit card. Instead, you talk to a machine that walks you through the steps.
State the card number, CVC (located on the back of the card) and expiration date when asked. Once the process is complete the verification is done and you can begin using your card. The CVC is important to know because it is what actually verifies the card. On Visa and Mastercards it is the small three-digit number on the right side of the back of the card, while on American Express cards it is the small four-digit number on the front.