[Q] Unable to add events to calendar topic

I have managed to open a calendar on my phone, but when I try to enter an event I get the message I have copied at the bottom of this box. I have tried adding accounts by clicking on "add account" but I am still get the same message when trying to add events. Please can someone explain exactly what is meant by "make sure that at least one calendar is visible"

Thank you

"Before you can add an event, you must add at least one Calendar account to your device and make a calendar visible. Touch Add Account to add an account (if you’ve just added an account, wait for it to finish syncing and try again). Or touch Cancel and make sure that at least one calendar is visible."