Make sure you have executed npm run setup-example-db once to have a populated example database. Otherwise, you will get 'no such table' errors.
Try some routes, such as /api/users or /api/orchestras?includeInstruments!
To experiment with POST/PUT/DELETE requests, use a tool for creating HTTP requests such as HTTPie, Postman, or even the curl command, or write some JS code for it with got, ky or axios.