Box means that you are dealing with real valued quantities.
The first array np.array([-1,0,0] are the lowest accepted values, and the second np.array([+1,+1,+1]) are the highest accepted values. In this case (using the comment) we see that we have 3 available actions:
- Steering: Real valued in
[-1, 1] - Gas: Real valued in
[0, 1] - Brake: Real valued in
[0, 1]