Theory:

Collective nouns are names for an assemblage of a number of people, animals or things. Words like bunch, pride, flock and swarm are collective nouns. 
Collective nouns are words that are made up of more than one person, thing, place, animal or idea. You can’t have a team without individual members; we discuss a team as a single entity.
Example:
People: board, choir, family, group, jury, panel, staff
Animals: herd, pod, swarm, flock, pack
Things: bunch, fleet, flotilla, pack, set, collection
Usage:
  • A collective noun can be singular or plural, depending on the context of the sentence.
  • Always notice that each individual who is part of the collective noun is doing the same action at the same time who are part of that collective noun.
Example:
1. Every evening, the pack follows its leader to the river for water.
(The pack is a singular collective noun. "Follows" are a singular verb, and the word "its" is a singular pronoun)
 
2. After four hours sitting in the courtroom, the jury stretch looks at their watches and head for lunch.
(The jury is a plural collective noun in this example. Stretch, look and head is plural verbs and 'their' is a plural pronoun)