Getting Started
Mixxx is a DJ tool that allows for the playback and mixing of digital music (MP3, Ogg Vorbis, and Wave).
The basic requirements for Mixxx are a pc or laptop with a reasonable amount of storage space on the hard drive for your music, at least 1 audio card for outputting the sound and a way of controlling the software either by mouse, keyboard or a hardware DJ Controller.
Mixxx will run on the Linux, Mac OS X and Windows operating systems
Before you download and install Mixxx consider what your set-up will be. Your PC\Laptop, Audio Output, Operating System an
Some common set-ups are
Laptop(Stand-Alone) Just a laptop and the software. Relying on the onboad sound card to output your audio Laptop with DJ Controller (Deck Only)
Laptop with DJ Controller DJ Controller (Audio & Deck) Laptop\PC with Vinyl Control (feature due in 1.6.0)
The ideal way for any DJ to mix live is to have 4 channels of Audio output. 2 for the main mix and 2 for cueing and previewing the next track you are trying to mix in. This means either having multiple soundcards or a soundcard capable of outputting 4 channels of audio.
If you have made a decision about hardware make sure you consider System Requirements and Hardware Compatibility
This is the Mixxx Wiki - 
Mixxx is a free and open-source DJ software.
Manual
Hardware Compatibility
Reporting Bugs
Getting Involved
Contribution Guidelines
Coding Guidelines
Using Git
Developer Guide
Creating Skins
Contributing Mappings
Mixxx Controls
MIDI Scripting
Components JS
HID Scripting