...
Any part of your logic can be limited to only apply for to a specific visitor segment. This means that visitors in that segment will get all your logic Use-Cases without segment AND the use-cases you defined for that segment, and the others will only get all your Use-Cases without segment.
First, create or select the Use-Case(s) you want to only apply for a specific segment.
Then go to the Settings tab and define the segment you want to use to connect them. There is a quick-segmentation dialog you can use, but otherwise, you must first create your segment in the Segmentation View and after select selecting them in the drop-down.
Then click on Save & Test, test the behavior before publishing in the test view and then publish.
...