There is SOC ENCOUNTER user guide which will let you how to use the encounter tool. You may find it at yoour installation directory called doc.
Also there is a command reference guide for the command used in the encounter tool
If you have Encounter Test tool installed, in the installation hierarchy there is a small test design that you can start your experiments with.
The path will be:
<ET install dir>/tools.lnx86/tb/tutorials/dlx
Regarding which document you can start with, I would recommend you to start with a Encounter Test quick start guide. you can find this pdf again in the installation itself at <ET install dir>/doc/dftqs (dftqs.pdf)