Like on any other view, you can use the left hand menu bar on the top left to switch views.
You can also double tap the day number on the left hand side to zoom in to the day view for that day.
To add a new event in your calendar you can do one of the following:
1) Tap on the '+' button at the top right. This will take you to the create event screen for the day listed at the top bar.
2) Long tap on one of the day's cells, an example event called (no title) will show for the selected day. If you tap on the + button here you'll be taken to the create event screen.
3) Long tap on an existing event, this leads to an example event called (no title) right below the existing event. If you tap on the + button here you'll be taken to the create event screen.
Copy and Paste
When you long-tap on an event, you'll see an action bar at the top to cut, copy, edit or delete the event. Once you copy or cut the event you can long tap on a day or existing event to paste your event.
In DigiCal's left hand menu > preferences > calendar views > agenda > event color, you can choose to use your event's color as the tab color, or as the background color.
As tab color:
As background color:
You can change the app theme to dark theme by going to DigiCal's left hand menu > preferences > general > theme > dark. Then the agenda view will look like the image below: