Normally I would have my observables in services that get subscribed to in components, but I bundled them all in one class for the convenience of this answer. I've listed comments explaining each step. I hope this helps. : )

import { Subject } from 'rxjs/Subject';



export class ClassName {

    // ------ Creating the observable ----------

   // Create a subject - The thing that will be watched by the observable

   public stringVar = new Subject<string>();



   // Create an observable to watch the subject and send out a stream of updates (You will subscribe to this to get the update stream)

   public stringVar$ = this.stringVar.asObservable() //Has a $ 



   // ------ Getting Your updates ----------

   // Subscribe to the observable you created.. data will be updated each time there is a change to Subject

   public subscription = this.stringVar$.subscribe(data => {

         // do stuff with data

         // e.g. this.property = data

   });



  // ------ How to update the subject ---------

   // Create a method that allows you to update the subject being watched by observable

   public updateStringSubject(newStringVar: string) {

     this.stringVar.next(newStringVar);

   }

   // Update it by calling the method..

   // updateStringSubject('some new string value')



   // ------- Be responsible and unsubscribe before you destory your component to save memory ------

   ngOnDestroy() {

     this.subscription.unsubscribe()

   }

}