best approach to call entries from two different sections
You can create one section called events with the different entryTypes small and big.

You'll fetch all events with

craft.entries.section('events')


when you want to fetch only small events you'll do

craft.entries.section('events').type('small')


and the same for the big one.

However you can call entries from multiple sections too

craft.entries.section(['smallEvents', 'bigEvents'])


I suggest you to read the docs these Cheet Sheets are a good place to learn templating too