laravel 5.6 fetching data from database to view

I'm facing an issue on understanding the content of the index function in the controller

I'm trying to get all the posts from my posts table into a view

my index function

public function index()
{
    $posts=\App\post::all();
    return view('MainViews.welcome',compact('posts'));
}

my view

   <div class="row">
    @foreach($posts as $post)
      <div class='col-md-8'>
        <div class="post"></div>
             h3></h3>
          <a href="#" class="btn btn-primary">read it</a>
          <p>
          </p>
        </div>
      @endforeach
     </div>

I'm getting Undefined variable error and highlighting @foreach

and I have a question when to use compact and when I can user an array

via Chebli Mohamed