In my words.....
An Evening of Recollection (Evenings) is like going on a two - three hours retreat. They are given by an Opus Dei priest either at a local parish or in an Opus Dei house. An Evening is held monthly and cover specific themes (IE: Fortitude, Living Advent, etc.) The purpose of an Evening is to help you remember to sanctify your ordinary life through your professional work, family life and recreational activities. (Professional work includes motherhood for women such as myself who stay at home with there children.)
The layout I am accustom is as follows: Priest begins with prayer and then gives a meditation, an examination of conscience (varies by month), a talk by a married member of Opus Dei, and followed by a second mediation given again by the priest. There is silence between meditation's and talk. Confession is offered before the Evening and between meditations. There is also have Benediction at the end.
Going to the Evening once a month is a beautiful way for me to remind myself to begin again. I need this monthly reminder because so often I have fallen off the boat by this point and even if I haven't it helps remember why I am living a Plan of Life.