How can i add a second camera that will be showing only specific gameobject in game window ?

I mean when running the game the main camera will show the player and the whole game view and the second Camera will display in a small window on the right bottom a gameobject only.

I want that the Camera child of the Cube will show the Cube all the time in a small window on the right bottom corner of the Game View. So when i'm running the game the Camera will keep showing the Cube. Now when i'm running the game i see only the Main Camera(The main camera is child of one of the thirdpersoncontrollers).