How does sociology define religion?And what are the 4 sociological classifications within religion?

The sociology of religion refers to religion in society. 
Rather than looking at the truth or proof of
truth behind certain beliefs and practices, religious sociology simply looks
at what religions practice, where they came from (historically), how they have changed
and developed, and what are the common and universal themes among
them.

That said, the basic classification system for
sociology in religion is called the "church-sect typology."  It is broken down into four
sections:

1. The
   church: as an institution, the church is
   defined as a religion that embraces religious expression in society, provides a common
   worldview (how to live, etc.) for its members, and does not tolerate religious
   competition.  Examples at this level include the Catholic church, protestant churches
   (collectively), or
   Islam.


2. Denominations: within
   many churches there often exists different denominations.  Essentially, these sub-groups
   subscribe to one common belief (of the larger church) but disagree on smaller details
   and practices.  Examples at this level within the protestant church include Southern
   Baptist, Methodist, or
   Presbyterian.


3. Sects: sects
   are even smaller groups which form by breaking apart (typically) from a denomination. 
   Often, they are formed from discontent and disagreement.  Many evangelical (Protestant)
   Christian denominations have further divided into more specific sects.
   


4. Cults or New
   Religious Movements: like sects, cults are considered new religious
   movements, but rather than breaking off of an existing movement, cults most often form
   completely independently.  Rather than advocating a return to an existing "church" (or
   pure religion), cults claim to believe in something completely new as a result, many
   times, of long lost scriptures or new prophesies.  There have been small cults which
   make headlines through mass suicides or other radical (and often horrific) displays of
   unity, but there are also those who consider Jehovah's Witnesses or Mormons, for
   example, to be cults, because they base their beliefs off of
   additional scriptures and modern
   prophesies.

Sociologists href="http://fasnafan.tripod.com/religion.pdf">define religion according to
substantive qualities (an instution with superhuman beings (Spiro)) or functional
qualities (symbols that determine power and an order of existence
(Geertz)).