Bring up a PS prompt, and type $a = $env:windir
You just assigned $a to your Windows directory.
You could just as easily have done $a = C:\Windows, but I thought I'd throw 2 tips in for the price of one. :)
Just to verify, do:
get-childitem $a (or dir $a, or ls $a, or gci $a...)
and you should see the contents of your windows directory. Now here comes the fun part. Are ya ready?
pipe that to "out-gridview"
get-childitem $a | out-gridview
And watch what happens.
See the "Add Criteria" button at the top? Press it, select all the options. Cool eh??