GRANNY REMAKE questions

Hello guys, I don't know where to post this and I couldn't find answer on the internet, so here we go.

I beat this game long ago and I'm playing it again and there is a lot of added stuff that I can't figure out their purpose.

Items:

Cage key
Detail (1 and 2)
Pickaxe
Trampoline
Flare gun

I'm doing a practice run and I can't find a way to use them and I am getting a little bit frustrated tbh. Thanks in advance.