in bo 6.5 row level security

restric the rows in the table

In supervisor level, click on resource pane, select 
universe right click, on properties on, select rowlevel 

how many rows he want select that rows and apply ok

HI.. The above answer refers to Row limit where we can 
restrict users to run reports for specific row limits like 
5000 rows or 10000 rows just to have a good server 
performance.

where Row level security is allowing the end user who runs 
the report to view the data which he is authorized to view.

For Example you are trying to run a report which pulls data 
contaings of 2 departments of the organization.

If you belong to DEP 1 then you will see data related to 
DEP1 only and a user belonging to DEP2 can see DEP2 data 
only. if you belong to both the groups then you can view 
data without restrictions.

Yes you are right Kumar.

In Bo 6.5, the row level security can do in superviver 
domain but in Xi R2 the Designer can do since this future 
is implemented in Designer itself.