Laravel 5.5 about Model

I want to have a Chapter model that contains a district column contained multiple District model. But I have no idea how to link it. I just have done with model and migration.

class Chapter extends Model
{
  /**
   * The attributes that are mass assignable.
   *
   * @var array
   */
  protected $fillable = [
      'name',
  ];

  public function districts()
  {
    return $this->hasMany(District::class);
  }
}

class District extends Model
{
  /**
   * The attributes that are mass assignable.
   *
   * @var array
   */
  protected $fillable = [
      'name',
  ];

  public function chapter()
  {
      return $this->belongsTo(Chapter::class);
  }
  
  public function blocks()
  {
    return $this->hasMany(Block::class);
  }
}

What should I do after this? Do I need to mention the district in the chapter migration file?

Here is my migration file.

<?php

use Illuminate\Support\Facades\Schema;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;

class CreateChaptersTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('chapters', function (Blueprint $table) {
            $table->increments('id');
            $table->string('name')->indexed();
            $table->timestamps();
        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::dropIfExists('chapters');
    }
}

<?php

use Illuminate\Support\Facades\Schema;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;

class CreateDistrictsTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('districts', function (Blueprint $table) {
            $table->increments('id');
            $table->string('name')->indexed();
            $table->timestamps();
        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::dropIfExists('districts');
    }
}

Do I need to link them in the $fillable side?

via Chebli Mohamed