if you retrieve [column1 = ‘One’ and column2 = ‘Two’] this means you’re retrieving records for which both constraints are true. It does not retrieve records for which only one of them is true.
If you retrieve [column1 = ‘One’ or column2 = ‘Two’] this means you’re retrieving records that have either column1 = ‘One’ or column2 = ‘Two’ or both.
The ‘All’ / ‘First’ option is only relevant if a retrieve can have multiple results. If you know you’re retrieving only one record, or if you use sorting and want only the first one, or if you don’t care what object you get, you can select ‘First’ and have an object as a result of the retrieve instead of a list.