typeorm: what is the difference between getRepository() and getConnection()?

https://typeorm.io/#/select-query-builder/how-to-create-and-use-a-querybuilder

There are several ways how you can create a Query Builder:

Using connection:

import {getConnection} from "typeorm";

const user = await getConnection()
    .createQueryBuilder()
    .select("user")
    .from(User, "user")
    .where("user.id = :id", { id: 1 })
    .getOne();

Using entity manager:

import {getManager} from "typeorm";

const user = await getManager()
    .createQueryBuilder(User, "user")
    .where("user.id = :id", { id: 1 })
    .getOne();

Using repository:

import {getRepository} from "typeorm";

const user = await getRepository(User)
    .createQueryBuilder("user")
    .where("user.id = :id", { id: 1 })
    .getOne();

The documentation never explains the difference among these methods. When to use each method?