How can I perform a loop for each line of a file or string?
 

Use the Loop action. This can also be used to build one or more steps once for each record in a database, an XML document, a list, to explicitly assign values and process in a specified order, etc. See the Files.bld (repeat for file contents), XML.bld (process XML config data), Server.bld (process query results), and Advanced.bld (process list of values) samples for details.