Take a look at
this webpage, under "Bücher" you'll find the "Ersatzteilliste für Simson-Moped SR2e".
Picture 9a shows in which order the parts should be putten together.
The cones are adjusted in a way that the
wheel will run free, but without bearing clearence.
After that, you have to counter the flat axl nuts against the cones so that they won't change their position while riding, which can be a bit tricky:
You start on one side(I always countered the left side first) and then adjust the wohle bearing on the other - so turn back the adjusted cone on the right side about 45° and also fasten the nut. This "turning back" is necessary because with countering the nuts you will always reduce the bearing clearence.
After this process the break is mounted and the whole wheel can be installed.
Just try and be patient, this adjusting is very important!