return with errors laravel code example

Example 1: displaying errors in laravel

@if(count($errors) > 0)
<div class="p-1">
    @foreach($errors->all() as $error)
    <div class="alert alert-warning alert-danger fade show" role="alert">{{$error}} <button type="button" class="close"
            data-dismiss="alert" aria-label="Close">
            <span aria-hidden="true">&times;</span>
        </button></div>
    @endforeach
</div>
@endif

Example 2: $errors show this error in laravel

<input type="text" name="firstname">
@if($errors->has('firstname'))
    <div class="error">{{ $errors->first('firstname') }}</div>
@endif

Example 3: how to add an custom error to validater error in laravel

if (request('event') == null) {
    $validator->errors()->add('event', 'Please select an event');
}