OK I'll have a bash.
Your sensations of movement speed etc are only relative to what you see around you. So you are travelling in a car at 30mph, you are only doing 30mph relative to the road. The road is on the surface of the Earth rotating at approx 1000 miles per hour, the Earth is orbiting the Sun at approx 60000 miles per hour, so your speed is only 30mph relative to the road. Let's consider the train, we've all had the sensation of moving when the train next to us is in fact moving, that is because all you can see is the other train, no other reference points so you only realise what is happening when the train has gone and you see the station and you realise that you are in fact stationary.
Does that help? what don't you get? What it is saying, among many other things is that what you see and feel is relative to your view point.