I will suppose here, that you are running dataguard between your two or more database, and that you want to disable a physical running standby database. So, to do that, I suppose that you already enable your physical standby database with this command :
SQL> alter database recover managed standby database disconnect from session;
So, you have to first disable the automatic recovery mode of physical standby database. To do that, simply enter this command in sqlplus prompt :
SQL> alter database recover managed standby database cancel;
So, now your database is in mount mode, because it was in this mode before you get your physical standby database up to automatic recovery mode.
That's it, you can now, open or shutdown your database, and do maintenance of you system, or anything other, that recquire your standby database to be disable.