Based on your objective of fat loss whatever diet you follow should result in a caloric deficit of some sort. What that means for you will vary based on how much exercise you get both in a strict sense (at the gym or on the track) and a broad sense (do you sit at a desk all day or do you herd cats for a living).
Seeing that you want to gain muscle mass your diet should be rich in plant and lean animal proteins (i.e. legumes, grains like quinoa, chicken, turkey) and healthy carbs (whole grains). Healthy fats (avocados, nuts or fatty fishes) are also good and important because they facilitate a healthy metabolism but should be consumed in moderation. Eliminate unhealthy fat and refined carbs. That fried twinky isn't a good idea and neither is that slice of pizza and you know it.
Healthy eating is not rocket science. Stick to whole, unprocessed foods. Read your labels and understand what you are eating. The Whole30 diet has a great guiding principal in that regard: Read your labels and if you do not know what an ingredient is or does or where it comes from pass on it.