i want to check this code n give me the solution on that

you can iterate though the items using for each loop easily.
use meaning full variable names.

Dim query  As String
For Each item As String In listBox1.Items
     query   = "insert into TransactionCirculation(ForUserId)values('" & item  & "')"
     cmd = New SqlCommand(query  , con)
 
Next

you need to use executenonquery method, not the ExecuteReader, and also for each item you need to run
executenonquery, that means run executenonquery inside the loop. http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlcommand.executenonquery.aspx[^]

I see a few errors in this statement. First, as OriginalGriff pointed out, your For loop has an "index out of bounds" error. Next, you are creating a new SqlCommand for each item in your For loop, effectively overwriting the previous entries. You need to put the call to the database inside your For loop. Finally, you are using the ExecuteReader command when making an INSERT call. You should instead be using the ExecuteNonQuery[^] method, which is designed for INSERT statements.

Once you get through all of that, I think you need to look at your code design as well. There are a few issues that I think you should address. First, you use letters as variable names. This is not descriptive and it can lead to confusion later on, which can lead to the introduction of bugs into your application. Next, you are doing one insert per row. I'm not sure how big your list is, but that can be anything from inefficient to catastrophic. Instead, look at doing one INSERT statement that puts all of the values in at once. The actual SQL code would end up looking like this:

INSERT INTO Table(column)
SELECT ListItemOne
UNION ALL
SELECT ListItemTwo
UNION ALL
etc.

You would need to modify your loop to build a SQL statement like this, but the end result is one call to the database instead of multiple.