Career mode is what will get you started on Asphalt 8. There are a total of twelve (12) "seasons":
Tag Season
Season 1: Welcome
Season 2: More than Racing
Season 3: Street Rules
Season 4: Elite
Season 5: Injection
Season 6: Adrenaline
Season 7: Heat
Season 8: Airborne
MAX Season 9: Beyond
Exclusive Metal Events
Season 10: McLaren Legends Season (sometimes called Future)