You first take in the input through a prompt from the host. The raw guest list is taken in. PowerShell then splits the input string based on the commas and a regular expression match (necessary so it would work whether the input contains a space after the comma or not: not all users are alike). We use the -split and cast operators for the operation.

The loop part comes in at Foreach-Object. You pass the array object into the pipeline. The Foreach-Object cmdlet picks up the array, and processes one element at a time. When referring to the element within the loop, you use the $PSItem (a.k.a. $_) automatic variable, since the object has been passed through the pipeline.