Getting started with wearable development using nRF51822

Question

Hi, my first post here.
I'm a undergraduate student and newcomer to this field. I've some programming background but few in electronics and embedded systems (so probably this question will be to silly for most of us). 
 I would like to learn and understand how the building process of a wearable device (like a fitness tracker) works. 
 For this reason I'm planning to build a simple fitness tracker, based on nRF51822, just for understanding how this works, but honestly I have some difficulty to understand where to start.
Suppose I have a board with a pedometer, an heart rate sensor and nRF51822 on it. 
 How can I start programming the device? 
 What hardware and softwate I need? 
 What is the workflow of the building process? (for workflow I mean the different steps from the writing of the .c source code, up tho the debug and the upload of the firmware) ? 
 My goal is to understand how can I program and debub the firmware.
If someone could suggest me some resources, videos, tutorials, books and so on, I will appreciate a lot. 
 Thanks a lot in advantage.

endnode · Accepted Answer

Quite a wide topic, you could write a book!;) Try these two tutorials for newcomers: Nordic eBook about BLE development and nRF5 Getting Started guide . Once you master nRF5x architecture and firmware development (either based on Nordic's nRF5 SDK - which I recommend - or ARM mbed or other) then building basic prototype from development kits and breadboards/jump wires is usually enough to develop the basic functionality. Then if you would ever move to production it's long story of costom dev kits (simulating your platform in more compact form factor allowing debugging in almost real-life scenarios) and HW iterations, testing (functional testing like BLE DTM, power profiling, radio emissions etc.), certifications (typically FCC, ETSI, BT SIG, CE...), productization in some Contractual Manufacturer, Qaulity Control...