App Uart Question

[Definitely Confused]

I'm using the Nordic as a BLE solution, and it is just passing along data through the UART to another chip through the UART. However, I'm not sure how to just pass the data along using the example UART application from the SDK.

I am basically using the SDK example as is, but I've removed the APP_UART_DATA_READY code from the uart_event_handle callback. Right now, I'm testing it without having any data being returned via the UART, but the UART will be a two-way communication channel.

My two main questions are:

1. How do I differentiate between data sent from the main firmware via the UART and data received via the BLE destined for the UART?
2. What exactly is the app_uart_fifo doing?

[Definitely Confused]

I removed the data handling because it was just grabbing the data received over the nus_data_handler (because it was adding it via app_uart_put). I want the nus_data_handler to just pass the data along, and have the uart_evt_callback only handle data sent to the UART from outside my app