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:

Ctrl+Alt+T

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.

Alternatively:

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