Simple Mode is intended for making Sync easier for the end user as well as for saving some extra taps to make basic operations faster.
Simple mode can be turned ON/OFF in Settings > Advanced.
When Simple Mode is ON, all new shares are created in Downloads/Sync directory on phone's internal storage. Also it performs the following operations:
1. If folder with same name is already there, new one will be created with (1) index.
2. Hides hidden or system files in folder view.
3. Hides "Root directory" and "ExternalSD" directory in directory picker.
When Simple Mode is OFF, every time you add a new folder, you'll be prompted to select the share's location and will be able to pick SD card. Fo details about using SD card, please see here.
This is Resilio Sync guide. For Resilio Active Everywhere documention click here.