It uses MetaMask to interface with the blockchain.
Using MetaMask, import the account you are using with geth.
First, you will need to have the contract deployed on your blockchain. Make sure the ports are right in your truffle.js.
Run truffle deploy.
Now we will build the Dapp itself. Run npm install to get the necessary packages.
Now, once you have imported your account into MetaMask, run npm start.
A new browser window will open to localhost:3000, open the dev console to see what's going on. Submitting will open a MetaMask popup. Click confirm to send the transaction and register the device.