It's not a stupid question, it just doesn't have a simple answer!Pug308 wrote: or is this a really stupid question, and that's why nobody is replying?
The best answer is play around with it and ask questions about things you're not sure about, you're more likely to get a response to something more specific like "how do I read/clear the fault codes" than a vague "how do I use a Lexia and is there any documentation" type question.
As Mike points out its a dealer tool which was never intended for use by the general public - dealers will have received training on how to use it and have access to official support channels and documentation.
All Lexia's that we have are "grey market" at best, a lot of the documentation (which isn't really needed to use it) is only available through official channels or with the right logins to PSA websites, so we've all had to figure it out without the help of such documentation and share that gained knowledge with each other.
Another thing to check would be to browse some of the Lexia related threads on the forum and you'll find a bit of discussion about general and specific problems and issues.
I would start with trying to get a dialogue with the car in the global test mode under diagnostics to see if it will communicate with the ECU's and read their fault codes and go from there. Then at least you'll know its talking to the car and it only remains to learn how to use some of the more subtle features.
Reading and clearing fault codes, parameters measurements (viewing live data from sensors) and actuator testing (operate actuators manually) are the main useful features of a Lexia, although it can do other things as well.