Events on Google Calendar app not showing on Google Calendar website?

I usually use S Planner on my Samsung phone but I want to back it up. I downloaded the Google Calendar app and all the events from my S Planner are showing in it but (if for instance I lost my phone and needed to check my calendar) none of the events are showing up on the actual Google Calendar website once I sign in etc.

Does anybody know how I can get my events to show on the Google Calendar website?

Just because an event shows up in the Google Calendar app doesn't mean it's syncing to your Google Calendar account in the cloud. Google Calendar will also display events saved to the local Phone account (and presumably the Samsung account as well). These accounts don't sync to the Google Calendar account. In order to get them into your Google Calendar account in the cloud, you'd have to export the calendar to a .ical file, then import it to your Google Calendar: https://support.google.com/calendar/answer/37118?hl=en