Kdenlive is a free to download open source multi-platform video editing software.
Assuming you require the Debian distribution package, follow these simple steps.
To get started, open your terminal with:
Then, run the following commands one line after the other:
sudo apt-add-repository ppa:kdenlive/kdenlive-stable && sudo apt-get update
sudo apt-get install kdenlive
That's all you should need. Once the installation is complete, you should be able to open and run the program.
You can install it through the software centre, just search for "Kdenlive" in the software centre, and click Install.
Related: How to Install Lightworks on Ubuntu