If you have signals from the same domain but, nevertheless, want to show them on a different axis (e.g., to see the total and a snippet, side by side), then you have to create a new folder for the chosen signals.
To create a folder, you right click the view, choose "Add" and then "Folder". In the dialogue that now opens, you click "Dedicated Axis" and then add signals by dragging and dropping them to the folder.
Now you can vary the way that those signals are displayed from the others; for example, you can zoom in and out to gain a general overview of the signal or a close-up view of a section. A 'star' is added to the folder icon when you set the dedicated axis.