What is "development studies?"I am a student studying development studies and I don't understand the subject at all . Please explain what it is?

The word "development" in the field of development studies
refers to the development of countries that were once described as "Third World."  In
modern terminology, those countries are referred to as "developing countries." 
Development studies is concerned with studying issues that are particularly relevant to
that type of country.

To see what sorts of issues this
might include, you could look at the current issue of an academic journal in this field
(the sagepub.com link below).  You can see there are articles touching generally on the
issue of how to promote development in developing countries without ignoring issues of
social justice.  This is a common theme in development studies because countries often
pursue economic development without regard to social
justice.

There are also articles about such things as the
role of religion in developing nations and whether genetically modified crops are good
for sub-Saharan Africa.

Overall, then, we can see that
development studies covers a wide variety of issues.  Anything that is particularly
relevant to "developing nations" is a subject of study for someone in development
studies.