I'd definitely suggest you read the article that Bit Bucket pointed you to, but not until you understand how a Tally table actually replaces a loop in situations like this. Read the following article, first...

http://www.sqlservercentral.com/articles/TSQL/62867/

Then, make a permanent Tally table...

--===== Create and populate the Tally table on the fly

SELECT TOP 11000 --equates to more than 30 years of dates

IDENTITY(INT,1,1) AS N

INTO dbo.Tally

FROM Master.dbo.SysColumns sc1,

Master.dbo.SysColumns sc2

--===== Add a Primary Key to maximize performance

ALTER TABLE dbo.Tally

ADD CONSTRAINT PK_Tally_N

PRIMARY KEY CLUSTERED (N) WITH FILLFACTOR = 100

--===== Allow the general public to use it

GRANT SELECT ON dbo.Tally TO PUBLIC

After that, your problem suddenly becomes child's play, just like the article that Bit Bucket pointed you to...

--===== Simulate a passed parameter

DECLARE @Parameter VARCHAR(8000)

SET @Parameter = 'John[Sam]Will[Joseph]Smith[Joe]'

--===== Suppress the auto-display of rowcounts to keep them from being

-- mistaken as part of the result set.

SET NOCOUNT ON

--===== Get the items in the brackets and number them

SELECT ROW_NUMBER() OVER (ORDER BY N) AS ElementNumber,

SUBSTRING(@Parameter,N+1,CHARINDEX(']',@Parameter,N+1)-N-1) AS ElementValue

FROM dbo.Tally

WHERE N < LEN(@Parameter)

AND SUBSTRING(@Parameter,N,1) = '['