what is meant by application of dimenional analysis ?its about conversin of 1 system of unit to another

Dimensional analysis is not about converting from one unit
to another, its purpose is to ensure that the units on both sides of the equation
balance each other out, and to determine the relations amount physical quantities.  One
useful application of this is if you are stuck on a problem you can perform a
dimensional analysis of the variables in the equation to see what the dimensions of the
result will be.  From this you can ascertain what type of values have those dimensions
giving you a clue to what the equation solves.  With that it frequently becomes easier
to solve a problem as some context has been given by the dimensional analysis.  It is
also a good way to check your work to make sure that the units have worked out the way
they are supposed to.