how do I push object forward into direction it is facing?

Actually I want character to jump to direction he is facing, so how do I push it a little bit into direction he is facing right now?

if(Input.GetKey(KeyCode.Space))
{
rigidbody.AddForce(transform.forward); // you may need so set x,y,z seperate if no Vector3 overload, also assuming you object is properly oriented, other try transform.right or transform.up
}

Maybe you can use:

if(Input.GetKey(KeyCode.Space))
{
    rigidbody.AddForce(0, 0, pushForce);
}