How do I create a user-input column in SSRS?
1) How to create a column to input user data and after that I need to
  perform some operations on data enter by the user which i need to
  display in another column


SSRS is not creating an application, just a report. It is not advisable to use SSRS to collect user input. A limited amount can be done using parameters but this is on a per report basis not per row as I think you're implying in the question. For example you could have a parameter to multiple values by a common factor and then display that result.


  2)how to make round a decimal to nearest integer ex 6.03 to 6 and 6.52
  to 7


Create an expression with the Round() function.

=Round(6.03)


this returns 6. Round also accepts a second value for number of decimal places. But instead of literal value, your fieldname would be in the parentheses:

=Round(myFieldName)