Scale look like this for me with s-> shift z -> z
If I use G -> type in negative 1 so it´s works perfectly and exactly center so I can use it instead?
Look like this:
I don´t know why extra bone is visible here. I can only see Armature and not single bone but I think it´s same. Extra bone follow with it so I can ignore it or remove it?
Ahh, yeah, you don't actually HAVE to move it by scaling to the cursor. I was just showing a different way of doing things.
Sometimes you will find that that technique is the easiest/fastest way to move your bones in certain circumstances.
You might be having issues with your pivot point, or the orientation mode might already be in global so when you press Z that second time it switches to local.
But if you moved it 1 unit on the Y axis and you shift it back -1, that is another perfectly acceptable way of achieving the goal.
As for that extra bone. It looks like an error so it's probably safe to delete it. It's not good practice to leave useless parts hanging around your rig, however, you should make sure that it is an error first!! Otherwise you'll be swearing at yourself if it was needed.
But making these types of errors is actually part of improving - so don't swear too much at yourself.
Hope that helps.