I can't get iMovie for my Mac
I have a MacBook air Mid 2011(OS X El Capitan, version 10.11.6)
How can I get iMovie for it?
MacBook Air
You will need to upgrade to High Sierra in order to download iMovie.
Before doing this consider that some of your applications that you are running now may not run on High Sierra very well.Do some research first ( Google it ) if you are relying on some apps to still function.
Get High Sierra here