aCalendar supports standard (alert) notifications, which are shown as regular Android notifications, and additionally for Google calendars, email notifications.
You can add notifications with the respective button in the event editor.
The maximum number of notifications depends on the calendar type: Google Calendar and most local calendars offers up to 5 notifications, while Exchange-based calendars often only offer 1 notification.
You can choose from many presets for the notification time (given as time before the event) or set a custom date/time.
For all day events, the notification time is stored as minutes before the event starts (midnight). Not all calendar types offer negative values (i.e. same-day notifications after midnight).
From the notification you can directly set the event to snooze at the preconfigured snooze duration (or always be prompted). Snooze (and other actions in Android notifications) is usually only automatically shown for the top-most notification, for all others you need to expand the notification, by either tapping on the notification header or swiping down on the notification with 2 fingers.
When you open an event, you can also snooze (new in version 2.1) and you see, edit and delete any currently active snooze.
Snooze times marked with a ! indicate that the snooze time is later than the event start time.
Can be configured here: Settings / Notifications / Events / Snooze default time
You can set aCalendar to automatically re-notify you of events, when the notification hasn't been dismissed so far (new in version 2.1).
If you previously used the insistent option (removed in Android 8 by Google), this might be a good replacement.
You can set the default notification time(s) for timed and all day events in event defaults and editor settings.
You can set the sound, vibration, snooze and more in notification settings.
If you experience problems with notifications, best try the TEST button in notification settings first. It detects most common issues. Also try if the stock calendar app issues notifications correctly.
In most cases of notification problems, the notifications are blocked by too agressive energy saving options or 3rd party apps.
If you see unwanted default notifcations added to your events shortly after they are created, this is caused by Google Calendar upon synchronization. Please turn off the default notifications in Google Calendar (in the app or desktop web interface).