Very simple Sliverstripe GraphQL schema set up (assumes you have installed silverstripe/frameworktest)

company.yml

# app/_graphql/models/company.yml
SilverStripe\FrameworkTest\Model\Company:
  fields: '*'
  operations:
    '*': true

graphql.yml

# app/_config/graphql.yml

---
Name: app-graphql
After: '#graphql'
---
SilverStripe\GraphQL\Schema\Schema:
  schemas:
    default:
      src:
        - app/_graphql

SilverStripe\Core\Injector\Injector:
  SilverStripe\GraphQL\Schema\Schema.default:
    class: SilverStripe\GraphQL\Schema\Schema
    constructor:
      schemaKey: default
  SilverStripe\GraphQL\Controller.default:
    class: SilverStripe\GraphQL\Controller
    constructor:
      schema: default
      handler: '%$SilverStripe\GraphQL\QueryHandler\QueryHandlerInterface.default'
  SilverStripe\GraphQL\QueryHandler\QueryHandlerInterface.default:
    class: SilverStripe\GraphQL\QueryHandler\QueryHandler
    properties:
      Middlewares:
        httpMethod: '%$SilverStripe\GraphQL\Middleware\HTTPMethodMiddleware'

SilverStripe\Control\Director:
  rules:
    'graphql':
      Controller: '%$SilverStripe\GraphQL\Controller.default'

# Add a description to the Company
SilverStripe\FrameworkTest\Model\Company:
  class_description: Companies are big businesses.