The mostly used parts of the oscilloscope are volt/div and time/div settings. The magnitude of the incoming signal may be too big or too small for the window. Moreover, you may want to observe the signal in bigger or smaller intervals. To observe the signals as you want, you need to change the volt/div and time/div settings.
As mentioned before, the time/div settings is global whereas the volt/div settings change from signal to signal.
When you pinch to zoom on the scope area:
If the zoom includes horizontal movement, you scale the time/div.
If the zoom includes vertical movement, and there is no selected signal, you scale the volt/div of every signal.
If the zoom includes vertical movement, and there is a selected signal, you only scale the volt/div of the selected signal.
Another method to change these settings is to tap on the axes.