Have a look at this sticky thread in the Technical Discussions section on this forum: http://www.myoutlanderphev.com/forum/viewtopic.php?f=10&t=1278
It's a collection of Mitsubishi training material that describes the operation of various systems very nicely. As said above, there are different modes depending on the power demand, battery charge level and road speed. This is fundamentally a hybrid car that expects the engine to be used at least some of the time. It can run as a pure battery EV vehicle, but it isn't really designed primarily for that. It can run as a pure petrol vehicle, but it's not designed for that either (it'll keep charging the battery and switching to powering the wheels by electricity every time it's generated enough charge anyway even if you try). On longer, faster journeys you'll find it's in parallel mode mode of the time (engine driving front wheels and charging battery, with occasional switching back to electric power, with electric power to the rear wheels when required). On country roads with lots of accelerating and braking you may find it's using series mode to get more power to the wheels than electric alone can do. (EV is 60kW to the wheels maximum, series is about 120kW and parallel is up to 142kW).
I have to confess that I read all this before buying my Outlander PHEV, but that's the sort of person I am. I also read loads on Audi forums about the A3 e-tron, and BMW forums about the 225xi PHEVs before settling on the Outlander PHEV, after reading loads of reviews of different hybrids, BEVs and PHEVs on car review sites to narrow it down to those three. This is to get an idea of what people don't like about the cars and what to look out for when buying second hand. I also read the brochures and owner's manuals for the them too so I could see if there was anything I didn't like how it worked or some feature that I'd really like. As it was I wanted the Audi's dashboard and features, the Mitsubishi's powertrain, boot and height and not a lot from the BMW... I tend to do this sort of thing with any expensive purchase though, but I know some people are a lot more impulsive and prefer to figure things out rather than read about them beforehand. My daily job relies on knowledge of IT systems, so I'm in the habit of reading up and being well informed rather than reacting to issues with no idea of how to deal with it. Not everyone is the same - life would be boring if we were!