建议你去composer官网阅读一下Getting Started

借用小黑豆同学的代码，希望可以帮到你。
下面是一个User model，继承了IdentityInterface接口， 里面有login验证方法

class Users extends \yii\db\ActiveRecord implements IdentityInterface {
    public $rememberMe = false;
    public static function tableName()
    {
        return 'users';
    }
    public function rules()
    {
        return [
            [['username', 'email', 'password', 'create_at', 'status'], 'required'],
            [['create_at'], 'safe'],
            [['status'], 'integer'],
            [['username'], 'string', 'max' => 20],
            [['email'], 'string', 'max' => 40],
            [['password'], 'string', 'max' => 64],
            [['auto_key', 'access_token'], 'string', 'max' => 30],
            [['username', 'email'], 'unique', 'targetAttribute' => ['username', 'email'], 'message' => 'The combination of Username and Email has already been taken.']
        ];
    }

    public function attributeLabels()
    {
        return [
            'id' => 'ID',
            'username' => 'Username',
            'email' => 'Email',
            'password' => 'Password',
            'create_at' => 'Create At',
            'status' => 'Status',
            'auto_key' => 'Auto Key',
            'access_token' => 'Access Token',
        ];
    }

    public function scenarios()
    {
        return [
            'login'=>[ 'username', 'password'],
            'register'=>['username', 'password','email']
        ];
    }

    public function login()
    {
        if( !$this->validate() )
            return false;
        $user = Users::findOne( [ 'username'=>$this->username ] );
        if( $user==null )
        {
            return false;
        }
        if( $user->password != $this->password )
        {
            return false;
        }

        return Yii::$app->user->login($user, $this->rememberMe ? 3600*24*30 : 0);
    }

    public function register()
    {
        return true;
    }

    public static function findIdentity($id)
    {
        return static::findOne(['id'=>$id]);
    }
    public static function findIdentityByAccessToken($token, $type = null)
    {
        return static::findOne(['access_token' => $token]);
    }

    public function getId()
    {
        return $this->id;
    }

    public function getAuthKey()
    {
        return $this->auth_key;
    }

    public function validateAuthKey($authKey)
    {
        return $this->getAuthKey() === $authKey;
    }
}

然后再action里类似的代码如下（举例）:

class DefaultController extends Controller
{
    public $layout = 'basic';

    public function actionIndex()
    {
        if( !Yii::$app->user->isGuest )
        {
            return  Yii::$app->getResponse()->redirect('?r=user/main/index');
        }
        else {
            $model = new Users();

            $model->setScenario('login');
            if ($model->load(Yii::$app->request->post()) && $model->login()) {
                return $this->redirect(['/user/main/index']);
            }
            else{
                return $this->render('login', ['model' => $model]);
            }
        }
    }
}

这些代码当时我都看了，没有问题，model里的基本可以直接用，action是举例。

没有吧，几分钟就更新完了