In simple terms, its like when you go to a pizza place, and order a "Make your own" pizza - you pick the base, the sauce, the cheese, the toppings and when the pizza is done, you get exactly what you asked for.
There are three main ways to integrate with GraphQL in an existing microservices architecture.
In this blog post, I answer some common misconceptions and questions asked about GraphQL.
GraphQL is a way of asking for data from API - a query language for API. It offers a flexible way of asking for data, and you can get as much or as little data as you need.