Try the contract (Dapp) online here. To try this example locally, do:

truffle build
npm truffle migrate
npm run dev

Play with dapp.js and MyPing.sol and do a truffle migrate to deploy your MyPing Contract. The app.js can connect to an existing Ping (not MyPing) contract - so you dont have to set up a local blockchain - see line 4 and 5 of app.js.