Alright, let's get started with setting up Firebase Firestore and GraphQL for your web app. First things first, make sure you've got Node.js and npm (Node Package Manager) installed on your system.

To get the Firebase tools, just run this command:

npm install -g firebase-tools

And for the GraphQL server libraries, Apollo Server and GraphQL, use this command:

npm install apollo-server graphql

Next up, you'll need to log in to Firebase. Use your Google account for this. Just type the following command in your terminal and follow the instructions that pop up:

firebase login

Navigate to your project directory and run this command:

firebase init functions

You'll be asked to select the Firebase project you're working on. Once you pick it, the functions will be linked to your Firebase project.

Now, let's install some libraries you'll need to use GraphQL with Firebase Functions. Run this command:

cd functions && npm install express express-graphql graphql graphql-compose graphql-compose-mongoose mongoose cors

This will get you libraries like Express, GraphQL, Graphql Compose, and Mongoose, among others, which are essential for building a GraphQL API.

Create a new Firestore database and add some data to it through the Firebase console. Your GraphQL resolvers will be based on the structure of this Firestore database.

Now, let's set up Apollo Server for your project. Create an index.js file in the functions folder of your project. Write the Apollo Server schema in the index.js and also set up CORS.

const functions = require('firebase-functions');
const express = require('express');
const {ApolloServer} = require('apollo-server-express');

GraphQL relies on schemas and resolvers to handle requests. The schema is a model of the data that can be fetched through the GraphQL server, while the resolvers are functions that tell the server how to fetch the data.

Configure the schema and resolvers for your Firestore database in the index.js file.

Once the setup for GraphQL is done, deploy the firebase function to your project by running the following command:

firebase deploy --only functions

After the successful deployment, your GraphQL API is ready to be used in any front-end application. You can perform all CRUD operations using Apollo Client in your front-end application through this API.