annie3 wrote:
So the next question is, how do I get it on my desktop? I always had it until I got this new mini last fall and along with it , el capitan. I will research that, but if you know please advise. Also, I knew I could do one at a time, but I was putting together something that required 50 pics on 50 slides ! 😮
"So the next question is, how do I get it on my desktop?"
Get what? Keynote? You should have Keynote on your computer. Look in your folder on your Mac called Applications or do a spotlight search for Keynote. See below, I have two different versions of Keynote.

If you can't find Keynote see here
If i deleted keynote, can i reinstall it?
Also see here to make sure you are uptodate
How to update OS X and Mac apps - Apple Support

Also, have you just tried logging onto iCloud, click on Keynote, create your blank slides and drag your images over to the blank(s) yet?