Sure, in the Where clause I wanted to filter out some system folders.
With the -match operator you have a RegEx as the right-hand side operator.
In the RegEx expression you specify one or more 'masks' for which you want a match.
In the RegEx different masks can be separated by an OR (the | symbol).
In each individual mask you have some 'location specifiers', in this case the ^ indicates I want a macth at the begiining of the text.
I.e. '^abc' means match 'abc' at he beginning of the string. So 'abcd' will match, but 'xyzabc' will not.
There are some free learning resources available.
A good one is the Master PowerShell ebook. In Chapter 13 you find more info on Regular Expressions