Can somebody please make a shot & sweet tutorial telling how to forward an Internet connection to different network interfaces in Ubuntu...? This is the idea:

I'm using a 3G usb modem to get Internet on my laptop ,which is:

ppp0 IP=10.225.174.70

My Wifi device is:

wlan0 MAC=78:e4:00:d4:3d:85

These devices are determined from ifconfig command.

I want to share ppp0's internet connection with wlan0 device, so I can connect any other device to wlan0 and browse internet from that device.

Making a Hotspot using Network settings GUI doesn't do the trick because the other device won't receive Internet, it just connects to wlan0.

I heard iptables can do this, but I'm totally confused by the alien commands seen online. I'm no expert in networking. Please compose a clear & simple answer using the above devices. This is a huge annoying problem for iPhone & tablet users came to Ubuntu from Windows.