There is a good Angular Quickstart demonstrating this (fetching the token, making a backend/API call):
https://auth0.com/docs/quickstart/spa/angular2/02-calling-an-api#calling-the-api
const client = await this.authService.getAuth0Client();
const token = await client.getTokenSilently();
return this.httpClient
.get('/api/external', {
headers: {
Authorization: `Bearer ${token}`
}
})