Where to use Yon and Shi? And Where to use Nana and Shichi?

I've seen this, while learning Japanese Numericals, it was Yon for 四 or 4 but when ever I see someone count in Japanese, they say Shi, similarly while learning, 七 or 7 was Nana and whenever I see someone count they say Shichi. Please help me clear this confusion.

Also, tell me how to use them in non singular digits like how would you say 407 or 712 in Japanese.