Brought this article that was published by Wendel Birth that I found so you can see not only what it is more also how to use, maybe you understand better.

Link from where I got the reference for you to check the full article.: https://tableless.com.br/entendendo-rxjs-observable-com-angular /

What is an Observable?

By definition is a collection that works unidirectionally, that is, it issues notifications whenever a change occurs in one of its items and from that we can perform an action. Let's say it solves the same problem that the previous version of Angular had solved with $watch, but without using brute force. While in $watch we check our entire scope for changes after each $digest cycle (which has a great cost in performance), with Observable this check does not happen, because for each event a notification is issued to our Observable and then we treat the give.

What do I do with Observable? And Where does Angular come into this story?

Let's imagine the consumption of a web service, something very common in Single Page application, before Observable we would do this way

getUsers(): Promise<User[]>{
  return fetch(myApiUrl)
  .then(res=>res.json())
  .catch(err=> Observable.throw(err.message));

} The above code is quite simple, we are looking for a resource (a list of users) and after the answer we turn everything into JSON.

However, the new Angular was built with reactive applications in mind, abandoning the use of Promises and adopting default the Observable.

Using Observable the same function would look like this:

@Injectable()
class UserService {
 ...
 getUsers(): Observable<User[]> {
    return this.http.get(myApiUrl)
                    .map(res=>res.json())
                    .catch(err=> Observable.throw(err.message));
 } 
 ...
}