SQL Server 2005 - Calling User defined functions

I have created a user defined function that takes a string as input.

EG: Create function func_new(@str varchar(20))
returns varchar(20)
begin
......
//whatever code
.....

return @str1
end

@str is a table column(col1)
How do I call this function so that all columns in the table get manipulated by the function??
Do i have to write a stored proc to call this function or something else has to be done?

Have a read of the following article which will help you create and use your function. Read Me

You can apply a function to every row of a recordset by using the APPLY statement.

http://msdn.microsoft.com/en-us/library/ms175156.aspx

However, your function must be a table valued function, not a scalar function.