Need help about Query Bilder

I have read through the CI 4 docs but still confused about the query builder. Following code shows my current CI4 model:

PHP Code:

<?php
namespace App\Models;
use CodeIgniter\Model;

class TestModel extends Model
{

    protected $db;

    public function __construct( )
    {
        $this->db = db_connect();
    }

 private function checkData( $t, $v) {
 return $db->table( $t )->select()->where( $d )->countAllResults();
 }
} 


But I am little bit confused about the CI4 ways to get row or rows from database. In CI3 my code was:

PHP Code:

// Get rows
$query = $this->db->select()->from( $table )->where( $arr )->get();
return $query->result();

// Get row
$query = $this->db->select()->from( $table )->where( $arr )->get();
return $query->row(); 


Could you please help by write some demo code of the following two operations?

Thanks in advance.

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