The parochial vicar (capellanus) is clergyman serving as assistant (as to a rector) in a parish.
It is usually the equivalent to the internship, and young priest completing his formation is practice, but sometimes older priests are parochial vicars too. He can act only under the authority of the pastor or administrator. He is also called assistant pastor.
The pastoral associate is usually layman or laywoman, who helps the work of the pastor withor the power of the order.
The word curator could men either an administrator with priestly power or parochial vicar. Administrator of a parish can be layman or laywomen, he has delegated and limited responsibility.
As for the word vicar, the pope is the vicar of Christ and acts over the Church under His authority, the diocesan vicar is the vicar of the bishop, and usually acts over the diocese with the authority of the bishop, the parochial vicar acts over the parish under the authority of the pastor.