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
Create an expression with the Round() function.
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: