OK let's start.
I want to install simplescreenrecorder.
I go to search the package in the Debian web site: https://www.debian.org/distrib/packages
I set the search filters to stable, which corresponds to my current Debian system, Jessie. In case of you are using Debian 9 (Stretch) choose testing or sid to unstable packages... but the packages is not in the repositories, so I have to install it from somewhere else.

I google 'screenrecording' and the search takes me to the Ubuntu PPA: https://launchpad.net/~maarten-baert
On the page a click on the hyper-link "SimpleScreenRecorder" in the section "Personal package archives", and the page takes me to the PPA description: https://launchpad.net/~maarten-baert/+archive/ubuntu/simplescreenrecorder
Here is the program description:
SimpleScreenRecorder is a feature-rich screen recorder that supports X11 and OpenGL. It has a Qt-based graphical user interface. It can record the entire screen or part of it, or record OpenGL applications directly. The recording can be paused and resumed at any time. Many different file formats and codecs are supported.

On the description's page I click on "View package details" and the page directs me to the list of builds: https://launchpad.net/~maarten-baert/+archive/ubuntu/simplescreenrecorder/+packages

There is the link to every source version and the build status, for example:
simplescreenrecorder - 0.3.3-1~ppa1~vivid1
simplescreenrecorder - 0.3.3-1~ppa1~utopic1
simplescreenrecorder - 0.3.3-1~ppa1~trusty1 
simplescreenrecorder - 0.3.3-1~ppa1~precise1
[...]
There are more builds but the builder posts only a package for every version of Ubuntu.

I click on the first option: simplescreenrecorder - 0.3.3-1~ppa1~vivid1, and it expands the section "Publishing Details" on the page. Here is a copy of the section:

Publishing details

    Published on 2015-01-23

Changelog

simplescreenrecorder (0.3.3-1~ppa1~vivid1) vivid; urgency=low

  * Sorry, no changelogs yet.
 -- Maarten Baert (v2) <email address hidden>   Sat, 24 Jan 2015 00:19:07 +0100

Builds

    [FULLYBUILT] amd64
    [FULLYBUILT] i386

Built packages

    simplescreenrecorder A feature-rich screen recorder that supports X11 and OpenGL.

Package files

    simplescreenrecorder_0.3.3-1~ppa1~vivid1.dsc (1.9 KiB)
    simplescreenrecorder_0.3.3-1~ppa1~vivid1.tar.gz (1.5 MiB)
    simplescreenrecorder_0.3.3-1~ppa1~vivid1_amd64.deb (976.5 KiB)
    simplescreenrecorder_0.3.3-1~ppa1~vivid1_i386.deb (984.3 KiB)

With the RIGHT CLICK on the packages files copy the link location of teh packages: 
simplescreenrecorder_0.3.3-1~ppa1~vivid1.dsc 
simplescreenrecorder_0.3.3-1~ppa1~vivid1.tar.gz

As you can see we require the location of the descriptor (.dsc) and the source code version (.tar.gz)

Now, create temporary directory:
$ cd /

Create the working directory:
# mkdir wrk
$ sudo chmod 777 wrk
$ ls -hal /
$ cd wrk

Fetch the packages (Use the links copied):
$ wget https://launchpad.net/~maarten-baert/+archive/ubuntu/simplescreenrecorder/+files/simplescreenrecorder_0.3.3-1%7Eppa1%7Evivid1.tar.gz https://launchpad.net/~maarten-baert/+archive/ubuntu/simplescreenrecorder/+files/simplescreenrecorder_0.3.3-1%7Eppa1%7Evivid1.dsc

Now let's build it using sbuild:

Check out my guide to set up sbuild here: 
References:
Guide:
Build packages from source

I don't want interruptions during the process:
$ xscreensaver
I set almost everything to 0.

I am following the second option to build in accordance with the sbuild Wiki, section "Building Packages":
"Alternatively, you may pass in the '.dsc' file of a package generated by dpkg-buildpackage,
git-buildpackage, and so forth so that it may be built with sbuild. For example, to build sbuild from its
'.dsc' file, do the following."
Reference: 
Web: https://wiki.debian.org/sbuild

If you are using testing the command is: $ sbuild -d testing *.dsc

But we are building for jessie, so setup the command accordingly:
$ sbuild -d jessie *.dsc

The summary of the build process says:
Build Architecture: amd64
Build-Space: 82732
Build-Time: 571
Distribution: jessie
Host Architecture: amd64
Install-Time: 1204
Job: simplescreenrecorder_0.3.3-1~ppa1~vivid1.dsc
Machine Architecture: amd64
Package: simplescreenrecorder
Package-Time: 1837
Source-Version: 0.3.3-1~ppa1~vivid1
Space: 82732
Status: successful
Version: 0.3.3-1~ppa1~vivid1

And now there are more files in the directory /tmp/wrk, let's take a look:
$ ls
Output:
simplescreenrecorder_0.3.3-1~ppa1~vivid1_amd64-20150524-1347.build
simplescreenrecorder_0.3.3-1~ppa1~vivid1_amd64.build
simplescreenrecorder_0.3.3-1~ppa1~vivid1_amd64.changes
simplescreenrecorder_0.3.3-1~ppa1~vivid1_amd64.deb
simplescreenrecorder_0.3.3-1~ppa1~vivid1.dsc
simplescreenrecorder_0.3.3-1~ppa1~vivid1.tar.gz

Install the package with gdebi:
$ sudo gdebi *.deb

Run the program:
$ simplescreenrecorder

Always install .deb packages that are build to your operating system and your version.

SimpleScreenRecorder has a GPL license. This allows you to take the source from one environment and rebuild it for another.

Reference:
Topic: Install simplescreenrecorder on Debian.
Web: https://www.youtube.com/watch?v=l9rZ7FBSYCk


Record the screen and the audio simultaneously:

Is there a program to record the screen and the sound in the Official Debian repos, rather than simplescreenrecorder which works only with the option set to Analog Mono?

$ simplescreenrecorder

SimpleScreenRecorder settings: 
Source: Analog Mono

When listen to the recorded video the sound is in the two speakers and seems all right.


If you are willing to synchronize the sound and the video later on:

To record the screen use  gtk-recordmydesktop:
Installation:
# apt-get update
# apt-get install gtk-recordmydesktop

To record:
First, set up the UI to set the directory to save the recording file named as out.ogv.
Second step is to test the sound. Record the sound with gnome-sound-recorder. 

Putting all together:
$ gnome-sound-recorder &
Adjust the sound input level in the menu Open Volume Control.
Start recording and execute:
$ recordmydesktop --no-sound
or use:
gtk-recordmydesktop and disable the sound check.
Save the video and the audio.
The program recordmydesktop --no-sound program is going to record the screen with low brightness and is going to take a lot of time to create the file, but at least you could edit the brightness later on with any capable video editor.

To record screen cast I use Open Broadcaster Software (OBS) in Ubuntu, but I never built it on Debian. I am going to share with you a link because if want to give it a try:
Reference:
Web: https://obsproject.com/download#linux

There is another way to record, with Kdenlive:
Resources: 
Web: http://www.kdenlive.org/
Web: https://www.youtube.com/watch?v=1eHEAfNFJ0k 
But you know what, I am not going to install more video editors at the moment.

By the way, remember something, these strings on my posts like:
--apt-update --apt-distupgrade have symbols that appear to be em dashes, but in the real life are two single dashes.


