Crust API is a bridge connector bewteen chain and other offchain services, you'd better not run it seperately.
Based on express and polkadot-js/api, connecting a running Crust Node and hosting a RESTful api service.
Go to Crust Node, follow the README.
Make sure you have latest nodejs and yarn installed.
yarn
56666
ws://localhost:9944
yarn debug {API_PORT} {CRUST_WS_ADDRESS}
yarn build && yarn start {API_PORT} {CRUST_WS_ADDRESS}
Refer this to see how to build and run crust api with docker.
Refer to this for more api details.