An override temporarily replaces the end action of the targeted object.
If you fully understand what that statement means, then you know how to use overrides. You may make a mistake here or there using them, but you should be able to fix it by examining all of your links and overrides.
If you don’t fully understand what that means, or you if you only think that you understand it, then overrides will cause you endless navigation troubles.
Even if you do understand overrides, most times whatever you are using them for can be accomplished more easily and cleanly using a combination of chapter end actions, chapter playlists, and playlists.