It doesn’t matter which connection is used.
But keeping with the ‘norm’, the outer screw section would be neutral and the single bottom connection would be live.
As AC is alternating current, both terminals/connections will change/alternate. So, it really doesn’t matter.
EDIT: I would like to add that mains voltage can be extremely dangerous in the wrong hands and as you had to ask, I would advise you to get a professional in to help.
Martin