How to import component into another root component in Angular 2

I am trying to import component from one file another root component file. it give error as ..

> zone.js:484 Unhandled Promise rejection: Template parse errors: 'courses' is not a known element:

1. If 'courses' is an Angular component, then verify that it is part of this module.
2. If 'courses' is a Web Component then add "CUSTOM_ELEMENTS_SCHEMA" to the '@NgModule.schema' of this component to suppress this message. ("

   My First Angular 2 App

   [ERROR ->]"): AppComponent@0:31 ; Zone: ; Task: Promise.then ; Value: Error: Template parse errors:(…) Error: Template parse errors: 'courses' is not a known element:

My app.component.ts be like [root component file]

import { Component } from '@angular/core';
import {CoursesComponent} from './courses.component';

@Component({
  selector: 'my-app',
  template: '<h1>My First Angular 2 App</h1><courses></courses>',
  directives:[CoursesComponent],
})

export class AppComponent { }

and my courses.component.ts be ;

import { Component } from '@angular/core';
@Component({
  selector: 'courses',
  template: '<h1>courses</h1>'
})
export class CoursesComponent { }

while importing courses component from courses.component.ts file inside app.component i am not able declare directive inside @Component{}

directives:[CoursesComponent] giving error to me

Please advise solution over it.

You should declare it with declarations array(meta property) of @NgModule as shown below (RC5 and later),

import {CoursesComponent} from './courses.component';

@NgModule({
  imports:      [ BrowserModule],
  declarations: [ AppComponent,CoursesComponent],  //<----here
  providers:    [],      
  bootstrap:    [ AppComponent ]
})

For Angular RC5 and RC6 you have to declare component in the module metadata decorator's declarations key, so add CoursesComponent in your main module declarations as below and remove directives from AppComponent metadata.

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';

import { AppComponent } from './app.component';
import { CoursesComponent } from './courses.component';

@NgModule({
  imports:      [ BrowserModule ],
  declarations: [ AppComponent, CoursesComponent ],
  bootstrap:    [ AppComponent ]
})
export class AppModule { }

Angular RC5 & RC6

If you are getting the above mentioned error in your Jasmine tests, it is most likely because you have to declare the unrenderable component in your TestBed.configureTestingModule({}).

The TestBed configures and initializes an environment for unit testing and provides methods for mocking/creating/injecting components and services in unit tests.

If you don't declare the component before your unit tests are executed, Angular will not know what <courses></courses> is in your template file.

Here is an example:

import {async, ComponentFixture, TestBed} from "@angular/core/testing";
import {AppComponent} from "../app.component";
import {CoursesComponent} from './courses.component';

describe('CoursesComponent', () => {
  let component: CoursesComponent;
  let fixture: ComponentFixture<CoursesComponent>;

  beforeEach(async(() => {
    TestBed.configureTestingModule({
      declarations: [
        AppComponent,
        CoursesComponent
      ],
      imports: [
        BrowserModule
        // If you have any other imports add them here
      ]
    })
    .compileComponents();
  }));

  beforeEach(() => {
    fixture = TestBed.createComponent(CoursesComponent);
    component = fixture.componentInstance;
    fixture.detectChanges();
  });

  it('should create', () => {
    expect(component).toBeTruthy();
  });
});

above answers In simple words, you have to register under @NgModule's

declarations: [
    AppComponent, YourNewComponentHere
  ] 

of app.module.ts

do not forget to import that component.