Acquire all the items needed.
Install a distro compatible with the Pi 2 on the MicroSD Card.
Put Pi Together and connect all peripherals.
Boot and set up Pi.
Download Bittorrent Sync.
Start Bittorrent Sync and access the program via WebUI (Address located in Readme.txt)
Go through the setup and set the destinations for the folders that you want to be able to sync.
Send QR code or secure key to phone or other device.
Once that is done, you should be able to access data, from your USB/HDD/SSD connected to the Pi, from your phone.