Its really simple and straight forard, just click on the new item that you want to create, enter the details and click on save.
A clint which has clients is a reseller of course. Thats the same with ispconfig 2, only that we did not name them explicitely a reseller to be more flexible as poeple often had the problem that a client could not become a reseller in ispconfig 2.
The "old" ISPConfig2 structure is really good in my opinion.. why this distortion from the well consolidated scheme ?
Because many poeple complained about it and it is not scalable enough for multi server systems with hundreds or thousands of users.
If you like ispconfig 2, then stay with it. ISPConfig 3 is a different software and you can not compare it to ispconfig 2.