In UserGuiding, segmentation means to divide end-users into groups, or segments. Later on, each group you've created can be matched with a specific guide or a hotspot.
In this way, you can set the right coupling in which your guide appears before its right spectator.
For instance, when you create a guide to welcome people who've just signed in to your platform, its match should be "the new users segment". People who're already familiar to your platform, don't need to see this guide.
Here, you can pick any attribute from the existing ones, designate conditions and create your own segment.
For detailed segmentation, there is always an option of the custom attributes which are basically segmentation properties that you define yourself.