I'm not sure we understand your question. You don't really "close" a catalog except for when you exit Lightroom. If you don't want to work on what you have opened then you simply go to another folder or import some new images. Lightroom doesn't have the normal save and close routine like you have in Photoshop or other photo editors. Adjustments are saved in the catalog as you make them. The catalog contains a history of the adjustments and is only really saved when a backup of the catalog is done.
It's one of those things that you just have to become accustomed to when using Lightroom. All you have to do is import the images for the tutorials and experiment with them. When you are finished with them you can simply remove the folder of images from Lightroom. And you will be able to choose whether or not to keep the images on your hard drive.
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