"nth" means which part you want to access, it could be "1" for first part, 2 for second part etc. By default it splits on space, so the line in your code above would take the beginning of the line up until the first space character in the line.
You can also specify which character you want to split on, e.g.
!columns1 = !line.part(1,'.')
in case you wanted the part of the line before the first full stop (".").
"nth" means which part you want to access, it could be "1" for first part, 2 for second part etc. By default it splits on space, so the line in your code above would take the beginning of the line up until the first space character in the line.
You can also specify which character you want to split on, e.g.
!columns1 = !line.part(1,'.')
in case you wanted the part of the line before the first full stop (".").
