When you CTRL + S or click save in the menu, you're saving your "sub circuit" as a new chip. When you click new, you're creating a new circuit, not a new project, and this is where you use your previously saved chips. If you want to review the chip you made, place it in the work space, then right click on it and click view. If you want to edit it (maybe you've made an error and need to fix it), you open the menu, then go to library, and click on your chip there and then edit at the bottom.