ECU Tuning for dummies

Hey guys! I was looking to start tuning cars (starting from my own one) but i have no idea what im doing. I'm planning to buy the KESS V2 programmer but other than that i have no idea what to do with the file and etc. and videos are not helping (they are all over the place for me). Do you know any guides or video series on youtube i can watch? Any help is appreciated