Create the Service using CLI

ng generate service <service-name>

Structure :

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

@Injectable({
  providedIn: 'root',
})
export class <service-name> {

  constructor() { }

}

Create the Service Manually

To create a new service manually:

1. Navigate to your Angular project directory.
2. Create a new file, <service-name>.service.ts
3. At the top of the file, add the following import statement.

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

1. Add @Injectable() service

@Injectable({
  providedIn: 'root',
})

1. Add a class statement that includes the code for the component with constructor.

export class <service-name> {

  constructor() { }

}

1. Using service in component, first need to Inject in constructor like this :

   Add a private  ex : heroService parameter of type HeroServiceto the constructor.
   

// example
constructor(private heroService: HeroService) {}

  Next Import :

// example
import { HeroService } from '../hero.service';

1. Need to add in <app.module.ts> like this :

// example
@Component({
  /* . . . */
  providers: [HeroService]
})

and import in it.

// example
import { HeroService } from '../hero.service';

Reference :

Angular Service

Live Example :

Stack Blitz