Don't enable debug_mode if you have no idea what it does. Don't enable notices_display if you have no idea what they mean. Notices are nothing to be worried about - after all they're not error messages, but notices. They exist for the benefit of developers who understand what they can be used for. If they bother you, turn notices_display off.
From the
documentation:
Enable debug mode
CPG will show error messages which are normally suppressed. This is helpful in troubleshooting problems with your gallery or when asking for help on the CPG Support Forums. Turn this feature off if you don't experience problems.
Turn it on (option "Everyone") if you are requesting help on the coppermine support board, so the supporters can have a look at the debug output as well. Choose the option "Admin only" when troubleshooting on your own - debug output will be only visible when you're logged in as admin, regular users or guests won't see the debug output.
Display notices in debug mode
May be helpful to troubleshoot problems with your coppermine install - only recommended if you know a little PHP and you can understand the additional error messages this option shows. This option only applies if debug mode is enabled.
In the future, read the documentation before posting questions. Don't enable options if you have no idea what they do. At least if something unexpected happens, you could at least have looked up what the option you enabled is meant to be used for.