Connect to Wifi network with Raspberry Pi

Edit the /etc/network/interfaces file. You will need to use sudo when editing the file.

sudo vim /etc/network/interfaces

The contents of the file should have the following, where you have to substitute your_network and network_password are the ssid and the password of your network:

auto lo

iface lo inet loopback
iface eth0 inet dhcp

allow-hotplug wlan0
auto wlan0

iface wlan0 inet dhcp
        wpa-ssid "your_network"
        wpa-psk "network_password"

Restart networking to pick up the changes

sudo /etc/init.d/networking restart