How to write a stored procedure?

Based on your revised question and using abhinav's example ..

DECLARE @vLike as varchar(30)
set @vLike = '%' + @R_NAME + '%'
IF NOT EXISTS (SELECT * FROM Details WHERE R_NAME like @vLike)

However if you definitely want to split the string based on the delimiters then have a look
here[^]

and another method using PATINDEX[^]

A really indepth article about splitting [^]

Useful (ish) resource for learning about stored procedures http://www.mssqltips.com/sqlservertutorial/160/sql-server-stored-procedure/[^]

Actually the question should be more structured but i think i understand what you trying to explain to some extent. It's like you don't want duplicate values in that column [R_NAME]. What i will suggest is.
1. Create a Uniques constraint on that column [R_NAME] and use your code to catch any error thrown when user enters a value already existing.

2. Use a stored procedure as follows

Create Procedure Pr_DDetails
(
@No nvarchar(20), @r_name nvarchar(256)
)
As
Begin
declare @rname nvarchar(256),
select @rname = R_NAME from [TableName] where R_NAME = @rname
if(@rname IS NULL)
return 
Else
Insert Into [TableName] (NO, R_NAME) Values(@No, @r_name)
End

Let me know if you understand it as intended.