Add to app.module.ts:

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { FormsModule, ReactiveFormsModule } from '@angular/forms';        <--
import { AppComponent }  from './app.component';

@NgModule({
    imports: [
        BrowserModule,
        FormsModule,                                                    <--
        ReactiveFormsModule                                                <--
    ],
    declarations: [
        AppComponent
    ],
    bootstrap: [AppComponent]
})

export class AppModule { }