If your hardware has some sort of Cryptographic Hardware Acceleration you should make sure it is supported by your OS (OpenWrt) and enabled.
strongSwan is recommended IPsec implementation, though some of this documentation may be relevant for other configurations.
Once you set up a VPN server on your OpenWrt router, you (and the other participants) will need to install and configure a VPN client (compatible with the VPN server) on each of your host machines. For HowTos regarding that, you should read the documentation of OpenVPN!
You may setup openwrt as an OpenConnect VPN client or server. This is a protocol based on SSL/TLS and datagram TLS and is compatible with CISCO's AnyConnect SSL VPN.
Not secure! PPTP is broken since 1997. See poptop security message.
vpnccompatible with Cisco's EasyVPN equipment