Run truffle develop in one terminal session: truffle develop

Run tests: truffle test

Start development server: npm start

The start command will bring up the page at http://localhost:3000/

Enter a new value in the text field, click Submit or press enter to submit the form. MetaMask should reply with "Transaction confirmed!" If it responds with a nonce error, reset the account via MetaMask -> My Accounts -> Settings -> http://localhost:9545/ -> Reset Account.