How can i upload user details with firebaseAPI key using tokens while signing up new user?

Hi ran into a problem creating user nodes while signing a user up to firebase. In the ionic course we are signing users up using a http post method( Firebase Database REST API) which returns a token eg my authService code

signup( email: string, password: string) {
    return this.http
      .post<AuthResponseData>(
        `https://www.googleapis.com/identitytoolkit/v3/relyingparty/signupNewUser?key=${
          environment.firebaseAPIKey
        }`,
        { email: email, password: password, returnSecureToken: true }
      )
      .pipe(tap(this.setUserData.bind(this)
      )
      );
  }

this works great for signing the user up but I am confused how I would make a node on firebase for the users details while signing users up this way? any advice would be great very new to ionic and firebase