A virtual card is a payment card that only exists in a virtual form. You can use it to make purchases online.
You can’t use it to withdraw cash or make purchases at point of sale (like restaurant/café/shops). This is because it does not have a mag-stripe or chip for Chip & Pin – on account of not being physical.
Apart from that, however, a virtual card has a 16-digit number, an expiry, and a CVV like any normal card – and will share the balance of your physical card.
What is important to know, though, is that, whilst your virtual card will be linked to the same account as your physical card, this card number will be different. This means that you can spend online without worrying about security. Simply lock your virtual card whilst still using your physical card as normal.
As the virtual card remains stored on your phone (for as long as its valid) you have the security of not losing it. Unless you lose your phone!