how to connect to a vpn through airport extreme

The AirPorts are neither a VPN client or end-point, but instead, a VPN-passthrough device. That would mean that you would need to use a VPN client on your computer to access a VPN server at a remote location. The necessary traffic to establish the VPN tunnel and follow-on communications would just "pass through" the AirPort's firewall. The AirPorts support passthrough for VPNs based on IPSec, PPTP, or L2TP.

Is the AirPort Extreme the only router in your current network configuration? That is, is it connected directly to your Internet Broadband modem or to another router upstream of it? What is the name of the VPN client running on the laptop? Are you attempting to connect it to a corporate (site-to-site) VPN or to a remote access type VPN?