I used to have cc subscyption but now i dont. I have my old LR 5 on cd.
When installed, i Cant open lr catalog as its not backward compatibile. So what to do to use it?
Your CC catalog cannot be used in LR 5.
You could launch LR CC, write all metadata to XMP, and then import the photos into LR 5. There are some edits that will not transfer this way (edits involving new features in Lightroom CC), and many other items that will not transfer this way (collections, virtual copies, flags, edit history, books, slideshows, web pages, and probably a few other things).
But flags and other thins are the more important. Anyway how can I lounch CC as I dont have it anymore?
If you still have Lightroom CC on your computer, you can launch Lightroom CC.
As far as I know, flags and the other items I mentioned cannot be transferred via XMP.
You could purchase Lightroom 6 and use the Lightroom CC 2015 catalog.