Error running 'app':

Olá, criei os códigos conforme orientação da aula Criando a primeira Activity e inclui os seguintes códigos mas sempre da o erro: "Error running "app': No target device found."

                             MainActivity:

package com.example.agenda;

import android.app.Activity;

public class MainActivity extends Activity { }

                              AndroidManifest.xml

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:roundIcon="@mipmap/ic_launcher_round"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">
    <activity android:name=".MainActivity">
        <intent-filter>
            <action android:name="android.intent.action.MAIN"/>
            <category android:name="android.intent.category.LAUNCHER"/>
        </intent-filter>
    </activity>
</application>