just downloaded elements 12 online can't use photo editor says I need to download it off cd

Please share the screenshot of the error and at which point do you see this error?

This is how normal installation happens:

If your machine is a windows machine, you'd have downloaded a .exe (an executable) file and a .7z (an archive) file.

Please run the .exe file which would extract files from the archive. You can then run setup file from the extracted files & install application.

if you're on a mac machine, you'd have downloaded a .dmg file. Double-click .dmg to initiate the setup & click options/buttons on each installer screen as per your requirement.

Please feel free to reply incase the above doesn't resolve your problem.

thanks.

~ Shefali

You write that you "downloaded", but did you also install it?

What is your operating system?  What is the exact message you are getting?