1. To create an account on soldier front you simply go to www.ijji.com
2. To download the game you can only do that at www.ijji.com
at the moment since it has not yet 100% transitioned over yet.
3. and 4. To play and start soldier front you have to download the reactor on www.ijji.com
The transfer process isn't 100% complete yet so you will still have the full authority and service on ijji and not aeria yet.