Can't even install the thing

I'm stupid...I know very little about computers...and I'm too lazy to go through all the threads in the forum:

When I go to install it says: The chosen volume contains software which is newer than the software you are using (Installing will replace newer version with older one)

I click Continue and head over to Installation. I press install and then this f*cker shows up: You cannot continue. There is nothing to install.

So, my Mac is compatible with this program and all; is there some kind of software I'm supposed to download/update independently or smthg? Gah, I feel dumb....

 

What is "the thing" (program and version)?

Which Mac (hardware and OS version)?

Phil