Here's an example. Let's say you wanted to change the modification date of a file. There's no way to do this with the tools that come with Windows except for Powershell (or VBScript). To do it, you'd open up a PowerShell window and type in the following:
set-location D:\MyFolder sets the current folder to D:\MyFolder. Replace with the path that holds your file
(get-item Myfile.Dat).LastWriteTime = "2010-01-21" changes the modification date for file MyFile.Dat to Jan 21 2010
Statements like these can be put into a file and executed automatically if needed. PowerShell is based on an object pipeline and can also use traditional procedural statements that let you automate pretty much any kind of task you can think of.