Actually there is no documentation other than a user guide in the Help menu of Spark. It is very old, but still can suggest how to use main Spark functions. There are many new things in Spark, which are not described there. Well, programmers usually just program and someone has to write a documentation
OTR (Off-The-Record) is the encryption for the person-to-person chat when you don’t want someone to be able to read/sniff your chat (especially when server is not providing the SSL encryption itself). You can read more about it here http://en.wikipedia.org/wiki/Off-the-Record_Messaging How it works: you start a chat with someone and press the OTR button, then the other part has to agree that this chat will be encypted and then you have an encrypted chat until someone closes the window.
ROAR is the alternative for Spark toast popups (popups informing about a new message). ROAR has a different design and more options for customization (colors, position, duration). It will probably replace toast popups at some point.
You can find settings for both of these plugins in Spark > Preferences.