the job of a halfback is to defend the goals and pass it up to the forwards so they can score a goal.
do you mean right back the defensive part, if this is right then maybe i could tell u more about it cause I'm a RB , you will need to support the right midfielder from the flanks and you could sometimes cross from the flanks if you have the chance to assist the other player and the same you will need tosupport your centre defense and prevent the opposition attackers to attack from the flanks, that's all,
this is a historical formation since most national teams play 4-4-2 variations or at most 4-3-3 but in England the terms were still used up through the 1960s
in the 1925-era arsenal team a halfback would be a tradtional number 6 or 4, they would play in front of a back line of 3 including a withdrawn center-half who functions as a stopper. ultimately, it is a four-man midfield, sort of square-shaped, with the two halfbacks as mentioned and at least one if not two withdrawn or deep inside forwards (traditional number 10 or 8). the attack consisted of a center forward and two wingers or wing halves. so you're looking at 3-3-4 or a 3-2-2-3 if both inside forwards are withdrawn.
so, to answer you question, (finally!) the halfback would of course like all players now and then in the middle third of the pitch, link the defense and attack--full of running and passing. defending wise, this era does a lot of man-marking so i would say it would depend on the opposition. but since most other teams either played 3-3-4 or 2-3-5 the halfback would not pick up the winger except in certain parts of the pitch but most likely they would mark the other team's inside forwards.
the old "halfback" is now part of a ususally 4-man midfield, frequently diamond-shaped (France 98), with hardly any wide players of kind before the 66 world cup.