As stated above, RESEARCH. We can only give you so much advice in a forum post. Articles on stuff like this really go in depth and give you a better understanding of the theory behind this ****.
First, I would say its pretty damn hard to lose fat and gain muscle at the same time. You need to either commit to a bulk or cutting phase. You need to bulk up some and then cut the fat off. It all comes down to caloric requirements. To cut weight you have to expend more cals than you consume and vice versa for bulking. It's a lot easier to build muscle, then maintain that muscle whilst cutting. However, bulking and losing fat at the same time sounds like a prohormone cycle to me.
If your wanting to do this naturally, lift heavy weights and eat a lot of food. After 2-3 months change your diet around a bit and start cutting the weight.
This is such a complex question to answer because there is so many different factors. You have to realize that your body does not want to build muscle and could care less if it uses that for energy or fat. You can gain a lot of muscle and then do a **** ton of cardio and burn allll your hard earned muscle off. Focus on low intensity cardio like the bike or powerwalk etc.. this burns fat. You could do this while bulking to help keep off the bulking fat.. but eventually to achieve the -12 bf range your gunna have to tweak your diet and really dial it in. Ab's are made in the kitchen.
Hope this gave you a good idea of what to look for in your research!