This video is a bit long (55+ minutes), but it does a great job of explaining how a hybrid drive-train dramatically improves the gas mileage of a vehicle. It includes good visualizations of conventional Otto cycle and Atkinson cycle internal combustion engines (ICE) - this is important because the modern Atkinson cycle engine (as used in Toyota's Hybrids) provides much better mileage, but would be unpleasant to drive without the hybrid's electric assistance.
Note: Toyota's Continuously Variable Transmission (eCVT) is quite different from traditional CVTs, and has proven to be quite a lot more durable. Initially designed for their excellent Prius models, Toyota's eCVT has been scaled up for use in their minivan and SUVs.
There is also a brief discussion here of the economics of Plug-In Hybrids and why you should charge them at home (or work) daily.
FYI - our Toyota Sienna Hybrid is our 3rd Toyota minivan since 2002. It easily drives as well as the previous two, while giving us a 50% improvement in gas mileage.