Assuming you are asking how long a bike drivetrain will last before needing to be replaced, the answer is it depends. A bike drivetrain includes all the moving parts that make your bike go, including the chain, cassette, crankset, and bottom bracket. These components are all subject to wear and tear, and will eventually need to be replaced.
How often you need to replace your drivetrain components will depend on how often you ride, what kind of conditions you ride in, and how well you maintain your bike. In general, though, you can expect to need to replace your chain every 1-2 years, your cassette every 2-3 years, and your crankset and bottom bracket every 3-5 years.
Of course, these are just general guidelines – if you take good care of your bike and don’t ride it too hard or in too much mud/sand/gravel/etc., you may be able to stretch out the life of your drivetrain components even longer. Conversely, if you ride frequently in harsh conditions or don’t maintain your bike well, you may find yourself having to replace components more often.