To create a list of things, use
[,]. Place all single values to include in the list in between the square brackets and separate each with a comma.
All operators that work on lists can then perform actions on the newly created list.
["First", "Second", "Third"]
This simply creates a list of the three strings First, Second and Third.
If you want to have a field storing if somebody is from Germany, Austria or Switzerland, you could write:
p.nationality contains any ['de', 'at', 'ch']