Hey @Charlotte,
Googling function names and stuff will always be the case when customizing things, at least a little bit 🙂
But yes – we have two references that should help a bit more specifically.
First is the Function Reference here – https://theeventscalendar.com/functions/. These are all of the functions within the code. Make sure to never use a function that has “DEPRECATED: YES” under its name!
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The second resource is the plugin code itself. Simply open the files for The Events Calendar, and head into the /src folder. The code here is (mostly) commented well and organized, and if you head to src/functions/ you’ll find a bunch of specific functions that are quite handy.
I hope this helps!
Cheers,
George