To create your segments go to your Emails & Automations tab and click on Lists and Subscribers.
After that click on Add Filter on top of your screen to start adding filters to define your Segments. You can create as many as you want segments based on different criteria. You can also update an existing segment.
To view all Segments simply click on the Segments tab next to Lists.
Click on the button and choose a filter.... for example: Country is Austria.
Click on the Save As New Segment button
Fill out a Segment Name and click on Submit.
Your new segment is now available to see inside the Segments tab - and you can send messages to this segment: