Good evening Jakub,
Thank you for taking the time to write back.
Just to set expectations, as you might know, the scope of our support is mostly to get our customers started on the right track and to help them in case of issues.
Although we are pretty excited to see our customers customize the plugin to their needs, we unfortunately do not provide complete support for customization.
With that in mind, we do have quite a bit of documentation available to you: https://theeventscalendar.com/customizations/
You should be able to get the list of functions from: https://theeventscalendar.com/functions/
Have a good weekend,
Geoff B.