_Follow along with the video_ --- To work with the Chainlink VRF (Verifiable Random Function) in Solidity, we need to inherit functions from an **abstract contract** called [`VRFConsumerBaseV2Plus`](https://github.com/smartcontractkit/chainlink-brownie-contracts/blob/12393bd475bd60c222ff12e75c0f68effe1bbaaf/contracts/src/v0.8/vrf/dev/VRFConsumerBaseV2Plus.sol). Abstract contracts can contain both defined and undefined functions, such as: ```solidity function fulfillRandomWords(uint256 requestId, uint256[] calldata randomWords) internal virtual; ``` - When we call the `Raffle::performUpkeep` function, we send a request for a **random number** to the VRF coordinator, using the `s_vrfCoordinator` variable inherited from `VRFConsumerBaseV2Plus`. This request involves passing a `VRFV2PlusClient.RandomWordsRequest` struct to the `requestRandomWords` method, which generates a **request ID**. - After a certain number of block confirmations, the Chainlink Node will generate a random number and call the `VRFConsumerBaseV2Plus::rawFulfillRandomWords` function. This function validates the caller address and then invokes the `fulfillRandomWords` function in our `Raffle` contract. > 🗒️ **NOTE**:br > Since `VRFConsumerBaseV2Plus::fulfillRandomWords` is marked as `virtual`, we need to **override** it in its child contract. This requires defining the actions to take when the random number is returned, such as selecting a winner and distributing the prize. Here’s how you override the `fulfillRandomWords` function: ```solidity function fulfillRandomWords(uint256, /* requestId */ uint256[] calldata randomWords) internal override { //pick a winner here, send him the reward and reset the raffle } ```