OpenL2TP comes with a number of man pages. For convenience, they are available online. New users will probably find the Quick Start Guide a useful starting point.

openl2tp Describes the features of OpenL2TP. Start here if you are new to OpenL2TP.
openl2tpd Describes how to invoke openl2tpd, the userspace daemon running the L2TP protocol. openl2tpd may be configured for use as an L2TP Access Concentrator (LAC) or L2TP Network Server (LNS) or both. It supports most features specified in the L2TP Specification, RFC2661 such as AVP hiding, tunnel authentication and both Incoming and Outgoing calls.
l2tpconfig l2tpconfig is a command line application used to control openl2tpd. It communicates with openl2tpd using Sun RPC, optionally over a network. Features include TAB syntax completion, command history and context sensitive help.