Loading iMovie

The first thing is to make sure that you have sufficient space on your computer to download iMovie. In the menu bar click on the Apple logo>About this Mac>Storage to see how much free space that you have. You would probably need at least 5GB.

iMovie 10 is free and you can download it for free if you have or ever have had it on your computer but perhaps deleted it. You would need to be running either Mojave 10.14.6 or Catalina to get the current version. Should your computer be unable to run Mojave or Catalina, you still could get a free update of iMovie to the most current version that your Mac's operating system can run. (See procedure below.) Again, you would have had to have had iMovie 10 on your computer before in order to get the update.

If you never had iMovie on your computer then you cannot download the current version, or any version, unless you are running Mojave or Catalina.

It looks like you might be running Yosemite operating system. Upgrade that to Mojave or Catalina if you can and then see if you can download iMovie 10. Be aware that if you upgrade to Catalina none of your older 32bit applications will work and legacy media will not play on iMovie.

Here's the update procedure for iMovie 10 that can get you the highest version that your OS can run: To update/redownload iMovie 10, drag your iMovie 10 app from the Applications folder into the trash, but do not empty the trash. (You can skip that step if you had iMovie 10 on your computer before, but deleted it.) Sign in to the app store and open your purchases folder by clicking on your name at the bottom of the app store side bar. You will see your purchases displayed, including iMovie 10. Redownload/update iMovie from there. If not successful, drag your present iMovie app out of the trash (if you moved it there) and return it to the Applications folder.

-- Rich