Usually, the loading procedure is this:
1) Extend the lens.
2) Unlock and remove the back.
3) Flip down the pressure plate.
4) Insert new roll of film.
5) Insert film tongue into top slot of takeup spool. There might or might not be a set of arrows.
6) Advance film using either the serrated thumb wheel (not sure if this was on the early Rolleis) or the film advance. You might have to trip the shutter, which is why you have to extend the lens.
I usually let film wrap around the takeup one complete turn. Then I replace the back, lock and you can advance-trip the shutter until the frame counter reaches zero.
Are you sure it's a 35S? That's the Sonnar model and that was only made in Singapore, as was the 35T(essar). The first Rollei 35 had no letter designation, because they all were made with a Tessar.
I ask, because early in the Singapore production, a key part of the film advance used a nylon gear, which was prone to damage when a heavy-handed user reached the end of a roll of film and forced the film advance lever to the end of its travel.
That part was later replaced with a metal gear.