Audio card installation:
I remember I had to change an old card on Debian Etch, and required to find a driver to install the generic driver AC'97 Sound or something like  that, and it worked! Most of cards are supported and installed during the system installation.
References:
Topic: Install a Professional sound system in Debian. I also recommend you to take a look at the distro AVLinux.
Guide: KXStudio
Topic: Deal with drivers installation
Guides: Basic Networking, Webcam
Topic: Tasks related to software installation
Guides:
Build the Linux Kernel
DKMS (Dynamic Kernel Module Support)
Build packages from source
Topic: Software installation sources and options available
Guides:
Software sources available
Debian binaries
Debian source code
Source code & Debian forks source code

Test the soundcard:
I setup a USB sound card when installed system and tested it with an analog headset and recorded my voice with grecord and play the file.ogg with Rhythmbox.

Audio mixers:
GUI:
$ gnome-control-center
And look for the icon Sound

Next two programs are not Gnome specific but sometimes resolve a variety of sound configuration issues.

$ pavucontrol
And look for the icon for sound

Text based mode:
$ alsamixer

ALSA is an acronym of Advanced Linux Sound Architecture Driver Version k3.16.0-4-amd64.
References:
Topic: How it works: Linux audio explained
Web: http://tuxradar.com/content/how-it-works-linux-audio-explained
File: How it works_ Linux audio explained _ TuxRadar Linux.pdf
Web: https://en.wikipedia.org/wiki/Advanced_Linux_Sound_Architecture
File: Advanced Linux Sound Architecture - Wikipedia, the free encyclopedia.pdf

Audio Application types:
DAWs, Audio Editors/Players/Tools
Synths/Samplers, Drumboxes, Loopers
Effects
Notation/Score, Tabulature, Lyrics
MIDI/OSC Software
DJ tools, CD/MP3 tools
Accompaniment/Karaoke
Mixers
Algorithmic Composition
Sound Synthesis
Video Software (edit/capture)
Lesson/Training/Metronomes/Tuners
Development Tools
Miscellaneous

Get sound applications:
Many of these apps reside in the Official Debian repos
References:
Topic: Linuxaudio.org
Web: http://wiki.linuxaudio.org/apps/start
Guides: KXStudio, Record Sound Recorder, Manage traditional software repositories, Audacity.
Topic: Installing USB soundcard in Virtual Machines
Guide: KVM

