On your iPad, go to Settings>Mail,Contacts,Calendars>Default Calendar. Here, be sure you have selected an iCloud calendar as your default, rather than something else like On My iPhone or On My Mac. If you haven't, make this change, then enter a new calendar event on your iPad and see if it syncs to your calendar on icloud.com when you check from your computer.
If your settings are correct and it still isn't syncing, check the calendar on icloud.com to be sure it includes all events from your iPad calendar. If not, enter any missing events on icloud.com. When the calendar on icloud.com is up to date, go to Settings>iCloud on your iPad, turn Calendars to Off, choose Delete from My iPad when prompted, then after a minute or so turn Calendars back to On to sync your iCloud calendars back to your iPad. Then enter a new calendar event on your iPad and see if it syncs to your calendar on icloud.com now.