XDCC file servers are one of the common systems used in transferring files to people on IRC. 
People offer files through a  "bot" that lists files for download.These files are referred to as "packs" or "packets". You must message the bot with a command to send the packet number.  Here is an example of a typical XDCC server:


** 5 packs ** 5 of 3 slots open, Record: 195.4KB/s
** Bandwidth Usage ** Current: 2.3KB/s, Record: 174.6KB/s
** To request a file type: "/msg BOT04 XDCC send #x" **
#1 11x [ 41M] Artist-Album-2003-GRP
#2 12x [ 31M] Artist2-Album2-2003-GRP
#3 16x [ 55M] Artist3-Album3-2003-GRP
#4 22x [ 73M] Artist4-Album4-2003-GRP
#5 12x [ 15M] Artis5t-Album5-2003-GRP
** Brought to you by #Channel **
Total Offered: 137.7 MB Total Transferred: 1.28 GB

Each pack is listed with Total Gets, File Size and finally Description.

2. XDCC Commands

There are a few commands available to use with an XDCC server. 
The command you need to know in order to request a file is XDCC send. See this example: 

/msg BOT04  XDCC send #1

If there are available slots in the XDCC server, you should start receiving the file immediately. Most XDCC servers will have queues, be patient.

The other command is XDCC list. "XDCC list" can be typed into channel, to display all active packs, but some channels dont support this feature. To manually view the list of the XDCC server you can try messaging the XDCC list command like this example: 

/msg BOT04  XDCC list