The Arduino IDE is a free IDE provided by https://www.arduino.cc/ that makes it easy to write and deploy code on Arduino and Arduino-based boards like the Arduino Pro Mini. Before we start, you must install the Arduino IDE from the following link. You might have to select the correct version for your OS: 

https://www.arduino.cc/en/main/software

If you already have the Arduino IDE, make sure its version is higher than 1.6.4.

You will have to switch the Arduino IDE to your board type. These instructions are for the Arduino Pro Mini with ATMEGA 328 and you will have to adjust these depending on the board you use; to do so, follow these steps:

1. Open up your Arduino IDE. 
2. Arduino Pro or Pro Mini will be visible under Tools | board:*. Select it.
3. Under Tools | processor:* select the appropriate processor and frequency for your board.

Once this setup is done, connect the Arduino Pro Mini to the USB port on your computer using a USB-to-FTDI cable.