Sql-server – How to specify a display name in emails from SSRS subscriptions

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)

Get SSRS Datasources from ReportServer

I would also like to include the 'Connection String' at least

How can I display Data Source details with a SQL query?

TSQL for getting the Connection String of SSRS Data sources

-- Transact-SQL script to get connection string of all SSRS Shared Datasources.

/*
Let's say you want to move a database to an other SQL Server, but which of the SSRS Shared Datasources uses this database and must be changed afterwards?
With this Transact-SQL query for ReportServer database you get the connection string of all Shared Datasources,
to document the usage or to search for a specific server/database.

Please remark: Querying the ReportServer database directly is not a supported way.
Works with SSRS 2005 and higher version ReportServer databases.
Requieres select rights on the "Catalog" table in ReportServer database.
*/

-- Connection strings of all SSRS Shared Datasources
;WITH XMLNAMESPACES  -- XML namespace def must be the first in with clause.
    (DEFAULT 'http://schemas.microsoft.com/sqlserver/reporting/2006/03/reportdatasource'
            ,'http://schemas.microsoft.com/SQLServer/reporting/reportdesigner'
     AS rd)
,SDS AS
    (SELECT SDS.name AS SharedDsName
           ,SDS.[Path]
           ,CONVERT(xml, CONVERT(varbinary(max), content)) AS DEF
     FROM dbo.[Catalog] AS SDS
     WHERE SDS.Type = 5)     -- 5 = Shared Datasource

SELECT CON.[Path]
      ,CON.SharedDsName
      ,CON.ConnString
FROM
    (SELECT SDS.[Path]
           ,SDS.SharedDsName
           ,DSN.value('ConnectString[1]', 'varchar(150)') AS ConnString
     FROM SDS
          CROSS APPLY 
          SDS.DEF.nodes('/DataSourceDefinition') AS R(DSN)
     ) AS CON
-- Optional filter:
-- WHERE CON.ConnString LIKE '%Initial Catalog%=%TFS%'
ORDER BY CON.[Path]
        ,CON.SharedDsName;

Here's a query to add the data source name as well using your TSQL:

USE [ReportServer]
GO

SELECT CATALOG.NAME
    ,CATALOG.[Path]
    ,DataSource.NAME datasource
    ,CATALOG.[Description]
    ,Created.UserName AS CreatedByUser
    ,CATALOG.[CreationDate]
    ,Modified.UserName AS ModifiedByUser
    ,CATALOG.[ModifiedDate]
FROM [dbo].[Catalog]
LEFT JOIN (
    SELECT [UserID]
        ,[UserName]
    FROM [dbo].[Users]
    ) AS Created ON CATALOG.CreatedByID = Created.UserID
LEFT JOIN (
    SELECT [UserID]
        ,[UserName]
    FROM [dbo].[Users]
    ) AS Modified ON CATALOG.ModifiedByID = Modified.UserID
JOIN DataSource ON CATALOG.ItemID = DataSource.ItemID
JOIN CATALOG cat1 ON DataSource.Link = cat1.ItemID
WHERE CATALOG.[Type] = 2
ORDER BY [Path]
    ,NAME