1. Park the lawn tractor on a level surface.
2. Turn off the key and engage the parking brake.
3. Connect one end of the positive jumper cable to the positive terminal of the car battery.
4. Connect the other end of the positive jumper cable to the positive terminal of the lawn tractor battery.
5. Connect one end of the negative jumper cable to the negative terminal of the car battery.
6. Connect the other end of the negative jumper cable to a metal surface on the lawn tractor engine, away from the battery.
7. Start the car.
8. Let the car run for a few minutes.
9. Try to start the lawn tractor.
10. If the lawn tractor does not start, let the car run for a few more minutes and try again.
11. Once the lawn tractor starts, remove the jumper cables in reverse order.
Be careful not to touch the positive and negative terminals of the batteries together, as this could cause a spark and an explosion.
If you are uncomfortable performing this procedure, you can have it done by a qualified mechanic.