Easiest method

1. To get the wireless interface:
   iwconfig
2. (Optional) If it is not up enable it:
   sudo ifconfig wlan0 up
3. Scan for SSID:
   sudo iwlist wlan0 scan | grep ESSID
4. Create wpa_supplicant file (can wrap ESSID in double quotes if got space). If passphrase got special character just run wpa_passphrase your-ESSID and enter password manually:
   wpa_passphrase your-ESSID your-passphrase | tee test_network.conf
5. Connect to it:
   sudo wpa_supplicant -c test_network.conf -i wlan0
6. Confirm it is working with:
   iwconfig
7. End the process and connect it in background:
   sudo wpa_supplicant -B -c test_network.conf -i wlan0
8. Obtain D:
   sudo dhclient wlan0

Open Network

network={
  ssid="hotel_wifi"
  scan_ssid=1
}

WEP

network={
    ssid="Your_WEP_SSID"
    key_mgmt=NONE
    wep_key0="yourwepkey"
}

WPA/WPA2

Optional to add pairwise=CCMP or pairwise=TKIP

network={
  ssid="home_network"
  scan_ssid=1
  psk="correct battery horse staple"
  key_mgmt=WPA-PSK
}