Hi, when you go to the academy there's a learning path on how to build an events app: https://gettingstarted.mendixcloud.com/link/path/42
If you are new to Mendix, take a look at the Learning Paths on the Mendix Academy. They take you thought all the basics you need to build your first App.
https://gettingstarted.mendixcloud.com/link/path
As for what to put in your Events App, you’d need to speak to whoever has asked you to build the App to get their requirements.
Hope this helps.