&& is notoriously hard to search for on Google Search, but the best I\'ve found is this article which says to use -and.
&&
-and
Unfortunatel
It depends on the context, but here's an example of "-and" in action:
get-childitem | where-object { $_.Name.StartsWith("f") -and $_.Length -gt 10kb }
So that's getting all the files bigger than 10kb in a directory whose filename starts with "f".