The For Each action loops over a set of collections of items, setting a variable to each value and executing the contained actions.
Whenever you need to deal with a list of things (lines, files, volumes, numbers, etc), the For Each action is a good place to start.
Example #1: Split text into lines or substrings
For a complete macro using this Action, see:
MACRO: [FILE] Process Lines in Text File
Example #2: Get Capture Group for Multiple Matches
See Regular Expressions (RegEx) Examples