Google.
e.g., Google for "Linux program to edit videos". You will rapidly find mention of many video editor programs. That's how I found "Kdenlive", "OpenShot", and "Avidemux" - the three video editors (among many) that I decided were the best for my specific needs. I decided by going to each programs main web page, looking at feature lists, gazing as screenshots of the program in action, reading reviews, looking at Youtube tutorials on program use, etc.
Once you've decided you want to try one of these programs, it's usually as simple as typing something like the following on the command line:
"apt-get install kdenlive"
Of, if you're not savvy on the command line, you can click on "Package Manager" in the start menu and install it that way.
These commands above are dependent on the specific distro you are running. The above examples are for Debian-based distros (like Ubuntu, LinuxMint, etc.) FYI, when you click on "Package Manager" on a Debian-based distro that would fire up the "Synaptic" program under the hood. However, on a RedHat-based distro, that would fire up the "RPM" program.
In Linux, many programs are just wrappers for other programs. e.g., the actual program that installs "packages" (programs) on Debian is "dpkg". To make dpkg simpler to use, the program "apt" wraps around it. And to make apt easier to use (and to add a GUI), the "Synaptic" program wraps around apt. You can install what you want with any of these, depending on your knowledge and experience. And there are other ways to install stuff as well, but no need to go into that now.
