The Segger embedded studio terminal emulator does not support an input capability. For this, use a terminal emulator like PuTTy, Tera Term, or GNU Screen. Configure the terminal to connect to your board by a serial connection as instructed in Installing a terminal emulator.
I am compiling the source code from -ble-secure-bootloader/ using ARM GCC v7-2017-q4-major (7.2.1) and comparing it to ARM GCC v4.8.4, segger embedded studio (with inbuilt GCC - version not known) and keil v5.
The outputs from keil, segger embedded studio and ARM GCC v4.8.4 all work on the target device and produce a hex filesize of 66KB, the ARM GCC v7.2.1 version however produces a smaller hex file of 57KB and whilst it illuminates the LED on the target board, no other parts of the application function (which call 'softdevice' functions, i.e. functions that reside in an application that already resides on the embedded hardware), so it seems to be missing something or a lot.
A standard first program on an embedded platform is the blinking LED. Getting an LED to blink demonstrates that you have your toolchain set up correctly, that you are able to download your program code into the μC, and that the μC and associated circuitry (e.g. the power supply) is all working. It can even give you good evidence as to the clock rate that your microcontroller is running (something that trips up a great many people,... 2b1af7f3a8