When switching from Mac OS X to Linux, OpenShot is a great alternative to iMovie.
In order to install it under Debian 9 (the official repository contains Version 1.4.3-1.2) I was performing following steps:
$ wget https://github.com/OpenShot/openshot-qt/releases/download/v2.4.1/OpenShot-v2.4.1-x86_64.AppImage $ sudo mkdir /opt/openshot && cd /opt/openshot $ cp /home/martin/tmp/downloads/OpenShot-v2.4.1-x86_64.AppImage . $ chmod +x OpenShot-v2.4.1-x86_64.AppImage $ cd /usr/bin $ sudo ln -s /opt/openshot/OpenShot-v2.4.1-x86_64.AppImage openshot
Firtst, you download the app image. I'm using a tmp folder in my home dir. Second, I'm installing programs in /opt and then symlink from /usr/bin to the executables. Some people would rather use /usr/local/bin but as long as the path is in your $PATH you can install it wherever you want.
That's it. First time you run OpenShot it asks you if you want to create a desktop link (a link within your menu).