X-Axis Mirror not working?

i guess I´m doing something wrong but I don’t know what.
I create three bones for an arm( extruding one from the other) , duplicate them, scale -1 along X axis to mirror them and then i hit “X-Axis Mirror”.
then, when I select and move, let’s say the left forearm, the right forearm is supposed to move symmetrically with the opposite forearm but it moves alone.
Did I miss something?

ok you should activate x-mirror befor you start extruding your bones, then in front view extrude with shift+e for semmetrical extrude

Thank you!
I didn’t knew about shift+e, I was watching the BBB rigging tutorial and it seems the guy first create the bones in one side, then mirrors the whole chain and when he moves a bone, it’s mirrored duplicated one, moves too. I don’t know how is it done


He changed the names of the duplicated bones to end with “.R” instead of “.L”. You can either do it manually, or use W>Flip Left-Right Names. Blender uses the names of the bones to work out the bone on the right that corresponds to a particular bone on the left (and vice versa).