You need to configure a .env file in the backend directory. This are the infos about your wallet private key, blockchain endpoint and NFT contract address. Find here the .env template
MATIC_URL=
PRIVATE_KEY=
CONTRACT_ADDRESS=
PORT=3001
Configure a .env in the client directory. This contains the infuryId required for the WalletConnect API.
REACT_APP_INFURA_ID=
Configure a .env in the nfts directory. This contains the polygonscan API key required for the truffle-verify plugin.
POLYGONSCAN_API_KEY=