I get internet from my wireless wlan0 and I would like to forward it to eth0 which is connected to another laptop. How can I do that? Thanks.

The function that you want to enable is network routing. You want to turn your computer into a router.

Look up linux router in the numerous howto web sites. Google will help you to find these articles.

Please provide more details on your wireless and the computers. For example, do you have a wireless NAT router? Do you have a wireless and a NIC interface on the first computer? What kind of network interface do you have on your laptop?

If you have a wireless NAT router, but the laptop doesn't have wireless, then you can connect the computers via an ethernet cable (via switch or cross-over cable) and enable forwarding. In this situation you want the two computers on different subnets. If you want to share a wireless connection (and internet IP address), and don't have a NAT router, then you need to configure the firewall to perform the network address translation (NAT) in the first computer.