If you're just starting to use running as a fitness activity, it's best to begin on flat paved areas. These surfaces provide a more stable and consistent footing, which can help minimize the risk of injury as you adjust to running. Gently rolling terrain is also fine, but avoid very hilly streets initially, as they can be more challenging and may increase the risk of strain.
Grass tracks can be soft and forgiving, but uneven surfaces can lead to instability. Trails in wooded areas are great for variety and nature, but they can also pose tripping hazards. Starting on flat paved areas will allow you to build your endurance and technique before potentially exploring other terrains.