ORIGINAL:
The most basic components of a GraphQL schema are object types, which just represent a kind of object you can fetch from your service, and what fields it has. In the GraphQL schema language, we might represent it like this:
BETTER:
The most basic component of a GraphQL schema is the object type. An object type represents a kind of object by listing its fields and this object can be fetched from your GraphQL service. Using the GraphQL schema language, an object type can be represented like this:
EXPLANATION:
Using singular nouns makes it easier to write consistent sentences. For example, the “it” in the last sentence of the original phrase is singular but the passage starts out using plural nouns. The phrase “and what fields it has” is awkward and it also transitions to the singular.