Recording Audio from External Synthesizers

I would like to know how to record the sounds that are in my external synthesizer into FL studio 12 while I am playing the synthesizer at the same time, and also the audio settings requirements needed to achieve this. I would appreciate a step by step guide on where the cables go in the input/outputs that are specific to my synthesizer and interface. I've searched for video tutorials and have found none that are for FL 12. I am not very technical and would appreciate any help. I have a Roland XP-80 synthesizer and a Focusrite Scarlett 2i4 interface. Pictures would help too if possible!