I'm new to observable and im having a super tough time trying to understand how it works!

I have some code that is fetching a JSON file for data but im not getting it on my ngOninit, I'm assuming that its because the code is asynchronous. I want to setup an observable to subscribe to the data once it gets in, but im completely new to observable.

Here is the code;

```
fetch('./assets/data/vendor.json').then(res => res.json())
      .then(data => {
        this.vendorData = data.vendors;
        this.vendorService.setVendors(this.vendorData);
      });
  }
  ngOnInit() {
    this.filteredVendor = this.vendorService.getVendors();
    this.isfiltered = true;
    console.log(this.filteredVendor)
  }

```

Any Ideas on how i can accomplish this and any good tutorials or lessons you can point me to for learning about Observables?

Thanks for your help.