Make .env file in root directory, copy variables from .env.example and set according to your requirement.
Run following commands :
truffle compile
truffle migrate --network rinkeby
You need to deploy contract on rinkeby network in order to render it on Opensea. If you don't need Opensea rendering feel free to deploy on any network including local.
To test the contract run
truffle test
For local development you need to install ganache, please follow this URL for more information Ganache cli
Make sure you've Metamask installed and running on browser
npm install
npm run serve
npm run build