With the Finder active, from the File menu, select Find... .
In the Find window that opens, in the section under the heading "Search for items whose:", click the Name pull-down menu and select Visibility. The options in the next pull-down menu to the right will change accordingly; select either invisible items or visible and invisible items as you prefer.
You can make invisible folders visible all the time (not recommended) using
TinkerTool
You can also make make .hidden things visible by Booting from another drive.
You can hide things selectively using
AltoMac
About hidden files