GraphQL is a query language that provides developers with flexibility to retrieve data from APIs, and the GraphQL Content API supports Content Delivery API (CDA) and Content Preview API (CPA). A GraphQL schema comes with every Contentful space, which is based on the query language's content types. To use GraphQL with Contentful, you can use various tools and features such as GraphiQL, GraphQL Playground App, and accessing your space ID and Content Delivery API token in your Contentful space settings. The GraphQL Content API supports retrieving data from APIs, including single entries, multiple entries, draft entries, reference fields, query complexity limits, reusable queries, and more. You can also reuse queries by passing down variables to avoid writing new queries for every author or field change. Additionally, you can include or skip a field in a query based on a variable value, create dynamic queries with type safety, and check out Contentful's developer portal for guides, tips, and tricks.