I recently installed ST3 on my Mac, and installed a bunch of packages using Package Control but I couldn’t use those packages even though they were present in “Installed Packages” folder and were also showing up under Package Control’s List Packages.

But when I clicked on any package in Package Control’s List Packages, I got an alert saying “this package can’t be found”
I’m using OS 10.10 (Yosemite).
ST3 version is Build 3083.
I’ve added a screenshot if that helps.
Please help me.

This is a bug, fixed upstream via github.com/wbond/package_control/issues/923.

Basically, packages are installed in .sublime-package zip archives and finder doesn’t know how to open that. If you want to edit files in there, use the PackageResourceViewer package and create an override package, also outlined in the doc page above.