bitquipu's questions

I am new to Angular, to explain myself properly I am going to start from an example.
When we have the Firebase library installed in our project, we can call the information from the Users table as follows:

constructor(db:AngularFirestore){
db.collection('Users').valueChanges().subscribe((data: User[]) => {
  this.users= data;
  console.log(this.users);
 });
}

The valueChanges() method is responsible for listening to any changes in the database and updating them in the user view without the need to refresh it (this is when making a manual change on a certain field in the same Firebase database).

So, how can this result be achieved, if for example I am consuming an API Rest? If when making a direct change in the database, this change is reflected in the user's view without the need to refresh.

// users.service.ts
get():Observable<any>{
   return this.httpClient.get(this.API_ENDPOINT+'/users_location');
}

// user.component.ts
users: Users[]=[];
constructor(private userService: UsersService) {
   this.getTrailers();
}

getUsers(){
  this.userService.get().subscribe( (data:Users[])=>{
    this.users= data;
  });
}