When you either can think of any more examples or the list is too long you say "etc." at the end of the sentence. Other wise meaning "so on and so forth..." It stands for 'Et Cetera'.
1. When you do not feel like elaborating on anything. Especially when the aforementioned phrases do not link in any way whatsoever. You would end the thought with "etc." because well, you just realized...you're an idiot.