The sacrament of Reconciliation has three forms available. Here is how they are described by the USCCB:
a. The Rite for the Reconciliation of Individual Penitents—"The first [form] is the reconciliation of an individual . . . with a new emphasis on the demand for personal dispositions and on the relationship to the word of God. . . . This form of reconciliation is the accustomed one, but enriched by a greater awareness, seriousness, listening, and so to speak, by a new outpouring of divine love and our own inexpressible joy in the knowledge of being restored to divine life. . . ."
b. The Rite for the Reconciliation of Several Penitents—"The second way of reconciliation is that of a communal preparation followed by individual confession and absolution. It combines the two values of being a community act and a personal act. It is a preferable form of reconciliation for our people when it is possible but it usually presupposes the presence of many ministers of the sacrament and this is not always easy."
c. The Rite for the Reconciliation of Several Penitents with General Absolution—"Then there is the third way, a collective form of reconciliation with a single, general absolution. This form, however, is by way of exception, of necessity, in cases sanctioned by the bishops, and with the continuing obligation of individual [confession] of grave sins, that is, mortal sins, at a later time."
The form you're asking about is B which is often offered during Advent and Lent. As a group there will be a Liturgy of the Word with readings and a brief homily. There will be an examination of conscience. Then there are usually multiple priests stationed at various places in the church so that individuals can go to confession.