Welcome to the forum!
Yeah, the first couple times in Zwift, it’s a little odd to know where the route ends.
There’s always a bit of a lead in before the route starts. So even though your miles / kms start as soon as you start moving, the route usually starts a mile or two into the ride.
Take any of the Watopia desert routes for example. You start out in the middle of nowhere, then ride under the bridge and into the sprint. At the end of the sprint, you go under an arch; that’s the actual start of the routes. You have to get back to that spot for it to be complete.
All of the worlds and routes are like that. The start and end are usually a banner or arch of some sort. It takes a little getting used to when you first start. But after a while, you don’t even think about it. At least until some of the mountain routes, where you climb to the top, that’s where it starts, so you have to do the climb again to complete the route.