Whichever you want sounds like a good answer. You may have seen Input.GetAxis("jump") ins some tutorial, hence the confusion. GetAxis take a string depending on the Input Manager. By default, Unity defines a "jump" for the space bar, because it's often what you want, but feel free to either modify "jump" in the IM, or create your own.

well all the GetAxis is i detecting the key press so you need something like

 void Jump()

{ if(Input.GetAxis("Space") > 0) { animation.Play("walk"); rigidbody.AddForce(Vector3.up *JumpSpeed); }

} try seting your jump speed to something depending on the scale of your game