Saying the concluding prayer in the Liturgy of the Hours

One of the most confusing bits of the Liturgy of the Hours is the concluding prayer for the offices. There are lots of bits in different brackets, and the "long ending" (through our Lord Jesus Christ your Son, who lives and reigns...") is never included in the text. Can anyone clarify which bit is said at which offices? Does it depend on whether you are reciting it in common or alone? For example, today's concluding prayer at Lauds (Thursdays in Advent): > Show forth your power, Lord, and come
Come in your great strength and help us.
Be merciful and forgiving,
and hasten the salvation which only our sins delay.
(We make our prayer) through our Lord.
(Through Christ our Lord.)