What is there to know?
The basic idea is the plates can be changed around to get different reed responses, and the fabric flaps can be either under or over the plates to give another different set of responses.
I quite like the lig, and have a couple of different sizes, its well made, easy to use and holds the reed securely, while still being easy to get the reed where I want it on the mouthpiece. I find the springiness of the empty plates prevents me strangling the reed entirely, which I have atendency to do with a regular rovner type lig. At first mine gripped the thick inner plate very hard in the springy bit, and I needed the second plate to push it out, but over time its got easier to change them about as the mood strikes.
Mostly I use it without either of the plates in, and I find the sound a little less bright/ edgy with the fabric over the plate and in contact with the reed, but its not a huge day / night difference.
There is an instruction sheet on the rovner website, http://www.rovnerproducts.com/ediiinsert.asp
Its probably best to just play around with it and use trial and error to find the best set up for you, but there was a general description of the effects here
Having said that, if you search, there are lots of threads where people dont like the complexity of the ED ii much and think its not worth the money...but as you got it for free, its worth checking out. Just be carefull not to scratch a mouthpiece with it.