There are three different ways you can do this: by applying the Crop/Pad filter, using the Edit/Transform feature, or with ALT Cropping. Then, you can pretty much cut out all the unnecessary parts, like toolbars, desktop icons, background, and more. If you want to make a comprehensive tutorial, your best bet is to crop a standard Display Capture to only show the open window. Mainly, you won’t be able to capture any pop-ups or menus.
However, there are some limitations to keep in mind. Window Capture works great with games in windowed mode, allowing you to record multiple monitors at once.
Apart from a slew of built-in editing features, there are also third-party solutions for platforms like Windows. Luckily, there are several ways to do that with OBS Studio.