You can keep the planned journey, so that during the journey you get instructions on where and when to make transfers etc… But you do of course not need to buy any tickets, as you already have your ticket.
So you just walk to your bus stop, wait for the bus to arrive, and get on the bus. You do not even have to show your pass to the driver, you can just board through any door, and take a seat. Then when the bus arrives at Lancy Pont Rouge station you just get off the bus, walk to the train platform, and get on the train. And so on at every transfer. It is all very easy really.
All you need to travel on public transport in Switzerland is be in possession of something that shows you have paid for it. Your pass is that.
But in your case I would just walk to the Lancy Pont Rouge station, and not bother with traveling 2 stops on the 40 bus.