1. Services are mostly used in displaying datas from APIs
2. To generate a new service use ng generate service Services/SERVICE_NAME
3. services are injectable because they would be mostly called by other components
4. Injection of services can happen at three level
   • AppModule – Same Instance of Service Injected would be available across application
   • AppComponent – Same Instance of Service Injected at this level would be available in this component and all child component
   • Any Other Component – Same Instance of Service Injected would be available to this component and child component(not to parent component)
5. @Injectable is not needed if the Service is added in app.modules.ts

aboutus.component.ts

.
.
constructor(private objApi:ApiService) { 
    this.objApi.getDataFromRest();
  }
.
.

api.service.ts

import { Injectable } from '@angular/core';

@Injectable({
  providedIn: 'root'
})
export class ApiService {

  constructor() { }

  getDataFromRest()
  {
    return console.log("Data from Rest Method");
  }
}