Hi, welcome on this forum, where users try to help other users.
First of all you have to look for the JEM settings in Backend. There are additional rights for those who want to enterf events in frontend!
Then the easiest way to enter events or venues is the menu point "submit an event" "submit a venue".
But if you have the rights you find (at least) in the official joomla templates in the "simple list" menue on top right some icons with tooltips. The first one is to enter new events. Please start with this 2 possibilities and more and more you will find in other menues additional possibilities.
You can try on the demo here too.
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