The CASE statement for a calculated field or script step is generally preferred over a nested IF statement. Easier to read and manage.
These threads should help understand the usage and logic...
Google "case statement site:forums.filemaker.com"
The Computer Guy, Seattle
You can use the case function written like this:
Case (country = "USA" ; city & state & zip ;
country = "Canada" ; city & state & zip ;
country = "Mexico" ; city & state & zip ;
zip & city )
Or you can stay with the If function:
IF (country = "USA" or country = "Canada" or country = "Mexico" ; city & state & zip ; zip & city )
You can even be a bit more creative by using Pattern count to make the expression a bit simpler:
IF ( patterncount ( "USA Canada Mexico" ; country ) ; city & state & zip ; zip & city )
All three of these functions can be looked up in FileMaker help if you want to learn more about how they work.